Rogue optical network interface device detection

ABSTRACT

Techniques are described for identifying a rogue network interface device whose laser is not under control of a controller of the network interface device. The techniques identify the rogue network interface device based on reception of a predefined data pattern in a timeslot that is not reserved for any of the network interface devices without needing to disable upstream data transmission from the network interface devices during their assigned timeslots. The techniques also relate to a network interface device determining whether the network interface device is transmitting optical signals at a wavelength different than the wavelength that the OLT to which the network interface device is associated receives.

This application claims the benefit of U.S. Provisional PatentApplication No. 61/990,610, filed May 8, 2014, and U.S. ProvisionalPatent Application No. 62/004,027, filed May 28, 2014, both of which areincorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to networking, and more particularly,communication between an optical network interface device and an opticalline terminal (OLT) in an optical network.

BACKGROUND

Network interface devices permit a subscriber to access a variety ofinformation via a network. A passive optical network (PON), for example,can deliver voice, video and data among multiple network nodes, using acommon optical fiber link. Passive optical splitters and combinersenable multiple network interface devices such as optical networkterminals (ONTs), also referred to as optical network units (ONUs), toshare the optical fiber link. Each network interface device terminatesthe optical fiber link for a residential or business subscriber, and issometimes referred to as a subscriber premises node that delivers Fiberto the Premises (FTTP) services.

In some systems, a network interface device is connected with wiring toone or more subscriber devices in the subscriber premises, such astelevisions, set-top boxes, telephones, computers, or networkappliances, which ultimately receive the voice, video and data deliveredvia the PON. In this manner, the network interface device can supportdelivery of telephone, television and Internet services to subscriberdevices in the subscriber premises.

SUMMARY

In general, this disclosure describes example techniques for detecting arogue network interface device from a plurality of network interfacedevices in an optical network based on an optical signal that includes apredefined data pattern used for rogue network interface deviceidentification, where such an optical signal is received in a timeslotnot reserved for any of the network interface devices. In some examples,the techniques may detect which network interface device is the roguenetwork interface device without needing to disable upstreamtransmission from the network interface devices. Disabling upstreamtransmission may interrupt services for the subscriber devices of thenetwork interface devices for extended periods of time, and thetechniques described in this disclosure may be able to identify therogue network interface device without such service interruption.

In the optical network, a device such as an optical line terminal (OLT)assigns each network interface device with a timeslot in which totransmit upstream optical signals. A rogue network interface device is anetwork interface device whose laser is not being properly controlled bya controller for the network interface device, causing the laser tooutput an optical signal in unassigned timeslots. For instance, in arogue network interface device, even when a controller of a networkinterface device attempts to turn off a laser of the network interfacedevice, the laser may still output upstream optical signals, includingoptical signals in upstream timeslots not assigned to the networkinterface device.

In the techniques described in this disclosure, controllers ofrespective network interface devices may be configured to causerespective laser drivers to turn off respective lasers during timeslotsnot assigned to the network interface devices. However, even when thecontrollers cause laser drivers to turn off lasers, each controller mayoutput predefined data patterns to corresponding laser drivers. Fornon-rogue network interface devices, these predefined data patterns willnot propagate as optical signals, because the laser is turned off duringtime slots not reserved for the network interface devices. For the roguenetwork interface device, however, the predefined data pattern willpropagate as an optical signal because the laser for the rogue networkinterface device does not turn off during time slots not reserved forthe network interface devices.

The OLT may monitor a timeslot that is not reserved for any of thenetwork interface devices, and determine whether the predefined datapattern is received during this timeslot. Based on the receivedpredefined data pattern, the OLT may determine which network interfacedevice of the plurality of network interface devices is the roguenetwork interface device. In one example, the predefined data patternmay be a unique data pattern that uniquely identifies one of the networkinterfaces. In another example, the predefined data pattern may be adata pattern with a specified data transition density that the OLTmeasures and compares against a data transition density measured from anearlier data pattern to determine which one of the network interfacedevices is the rogue network interface device.

As described in more detail, the techniques described with respect toutilizing a predefined data pattern may be extended to multiplewavelength systems. Also, for some optical systems, the techniquesdescribe ways in which a network interface device may determine that itis transmitting at an incorrect wavelength, as an example of awavelength rogue network interface device.

In one example, the disclosure describes a method of rogue networkinterface device detection, the method comprising receiving a datapattern, embedded with a unique identifier, from an optical signalreceived during a quiet timeslot, wherein the quiet timeslot comprises atimeslot that is not allocated to any of a plurality of networkinterface devices for upstream transmission, and identifying a roguenetwork interface device from the plurality of network interface devicesas one of the network interface devices having a unique identifier thatis same as the unique identifier embedded in the data pattern receivedduring the quiet timeslot.

In one example, the disclosure describes an optical line terminal (OLT)comprising a memory configured to store unique identifiers of aplurality of network interface devices, and one or more processorsconfigured to receive a data pattern, embedded with a unique identifier,from an optical signal received during a quiet timeslot, wherein thequiet timeslot comprises a timeslot that is not allocated to any of aplurality of network interface devices for upstream transmission, andidentify, using the unique identifiers stored in the memory, a roguenetwork interface device from the plurality of network interface devicesas one of the network interface devices having a unique identifier thatis same as the unique identifier embedded in the data pattern receivedduring the quiet timeslot.

In one example, the disclosure describes an OLT comprising means forreceiving a data pattern, embedded with a unique identifier, from anoptical signal received during a quiet timeslot, wherein the quiettimeslot comprises a timeslot that is not allocated to any of aplurality of network interface devices for upstream transmission, andmeans for identifying a rogue network interface device from theplurality of network interface devices as one of the network interfacedevices having a unique identifier that is same as the unique identifierembedded in the data pattern received during the quiet timeslot.

In one example, the disclosure describes a computer-readable storagemedium having instructions stored thereon that when execute cause one ormore processors of an OLT to receive a data pattern, embedded with aunique identifier, from an optical signal received during a quiettimeslot, wherein the quiet timeslot comprises a timeslot that is notallocated to any of a plurality of network interface devices forupstream transmission, and identify a rogue network interface devicefrom the plurality of network interface devices as one of the networkinterface devices having a unique identifier that is same as the uniqueidentifier embedded in the data pattern received during the quiettimeslot.

In one example, the disclosure describes a method of transmission forrogue network interface detection, the method comprising transmitting,with a controller of a network interface device, data received from oneor more subscribers devices in timeslots assigned to the networkinterface device, and transmitting, with the controller, a uniqueidentifier used to identify the network interface device during one ormore timeslots to which the network interface device is not assigned.

In one example, the disclosure describes a network interface devicecomprising a laser driver, and a controller configured to transmit, tothe laser driver, data received from one or more subscriber devices intimeslots assigned to the network interface device, and transmit, to thelaser driver, a unique identifier used to identify the network interfacedevice during one or more timeslots to which the network interfacedevice is not assigned. Wherein the laser driver is configured totransmit the data received from the one or more subscriber devices intimeslots assigned to the network interface device, and transmit theunique identifier during the one or more timeslots to which the networkinterface device is not assigned.

In one example, the disclosure describes a method of rogue networkinterface device detection, the method comprising receiving, with anOLT, a data pattern in an optical signal received during a quiettimeslot, wherein the quiet timeslot comprises a timeslot that is notallocated to any of a plurality of network interface devices, with whichthe OLT is associated, for upstream transmission, determining that arogue network interface device from which the optical signal is receivedduring the quiet timeslot is not a network interface device to which theOLT is configured to transmit downstream data based on the received datapattern, and communicating with one or more other OLTs information toquarantine the rogue network interface device.

In one example, the disclosure describes an OLT comprising a memoryconfigured to store information, and one or more processors configuredto receive a data pattern in an optical signal received during a quiettimeslot, wherein the quiet timeslot comprises a timeslot that is notallocated to any of a plurality of network interface devices, with whichthe OLT is associated, for upstream transmission, determine that a roguenetwork interface device from which the optical signal is receivedduring the quiet timeslot is not a network interface device to which theOLT is configured to transmit downstream data based on the received datapattern and the stored information, and communicate with one or moreother OLTs information to quarantine the rogue network interface device.

In one example, the disclosure describes a system comprising a firstOLT, a set of network interface devices associated with the first OLT,and a second OLT. The first OLT is configured to receive a data patternin an optical signal received during a quiet timeslot, wherein the quiettimeslot comprises a timeslot that is not allocated to any of the set ofnetwork interface devices, associated with the first OLT, for upstreamtransmission, determine that a rogue network interface device from whichthe optical signal is received during the quiet timeslot is not anetwork interface device of the set of network interface devices basedon the received data pattern, and communicate with the second OLTinformation to quarantine the rogue network interface device.

In one example, the disclosure describes an OLT comprising means forreceiving a data pattern in an optical signal received during a quiettimeslot, wherein the quiet timeslot comprises a timeslot that is notallocated to any of a plurality of network interface devices, with whichthe OLT is associated, for upstream transmission, means for determiningthat a rogue network interface device from which the optical signal isreceived during the quiet timeslot is not a network interface device towhich the OLT is configured to transmit downstream data based on thereceived data pattern, and means for communicating with one or moreother OLTs information to quarantine the rogue network interface device.

In one example, the disclosure describes a computer-readable storagemedium having instructions stored thereon that when executed cause oneor more processors of an OLT to receive a data pattern in an opticalsignal received during a quiet timeslot, wherein the quiet timeslotcomprises a timeslot that is not allocated to any of a plurality ofnetwork interface devices, with which the OLT is associated, forupstream transmission, determine that a rogue network interface devicefrom which the optical signal is received during the quiet timeslot isnot a network interface device to which the OLT is configured totransmit downstream data based on the received data pattern, andcommunicate with one or more other OLTs information to quarantine therogue network interface device.

In one example, the disclosure describes a method comprising receiving,with a network interface device, one or more requests from an OLT todetermine whether the network interface device transmitted one or moreoptical signals during one or more timeslots assigned to the networkinterface device for upstream transmission, determining, with thenetwork interface device, that the network interface device transmittedthe one or more optical signals during one or more timeslots assigned tothe network interface device for upstream transmission, determining thatthe network interface device is transmitting the one or more opticalsignals at a wavelength that the OLT does not receive based on thedetermination that the network interface device transmitted the one ormore optical signals during one or more timeslots assigned to thenetwork interface device for upstream transmission, and the reception ofthe one or more requests from the OLT, and disabling the networkinterface device from transmitting upstream optical signals based on thedetermination that the network interface device is transmitting the oneor more optical signals at the wavelength that the OLT does not receive.

In one example, the disclosure describes a network interface devicecomprising a laser, and a controller configured to receive one or morerequests from an OLT to determine whether the laser transmitted one ormore optical signals during one or more timeslots assigned to thenetwork interface device for upstream transmission, determine that thelaser transmitted the one or more optical signals during one or moretimeslots assigned to the network interface device for upstreamtransmission, determine that the laser is transmitting the one or moreoptical signals at a wavelength that the OLT does not receive based onthe determination that the laser transmitted the one or more opticalsignals during one or more timeslots assigned to the network interfacedevice for upstream transmission, and the reception of the one or morerequests from the OLT, and disable the network interface device fromtransmitting upstream optical signals based on the determination thatthe laser is transmitting the one or more optical signals at thewavelength that the OLT does not receive.

In one example, the disclosure describes a network interface devicecomprising means for receiving one or more requests from an OLT todetermine whether the network interface device transmitted one or moreoptical signals during one or more timeslots assigned to the networkinterface device for upstream transmission, means for determining thatthe network interface device transmitted the one or more optical signalsduring one or more timeslots assigned to the network interface devicefor upstream transmission, means for determining that the networkinterface device is transmitting the one or more optical signals at awavelength that the OLT does not receive based on the determination thatthe network interface device transmitted the one or more optical signalsduring one or more timeslots assigned to the network interface devicefor upstream transmission, and the reception of the one or more requestsfrom the OLT, and means for disabling the network interface device fromtransmitting upstream optical signals based on the determination thatthe network interface device is transmitting the one or more opticalsignals at the wavelength that the OLT does not receive.

A computer-readable storage medium having instructions stored thereonthat when executed cause a controller of a network interface device toreceive one or more requests from an OLT to determine whether thenetwork interface device transmitted one or more optical signals duringone or more timeslots assigned to the network interface device forupstream transmission, determine that the network interface devicetransmitted the one or more optical signals during one or more timeslotsassigned to the network interface device for upstream transmission,determine that the network interface device is transmitting the one ormore optical signals at a wavelength that the OLT does not receive basedon the determination that the network interface device transmitted theone or more optical signals during one or more timeslots assigned to thenetwork interface device for upstream transmission, and the reception ofthe one or more requests from the OLT, and disable the network interfacedevice from transmitting upstream optical signals based on thedetermination that the network interface device is transmitting the oneor more optical signals at the wavelength that the OLT does not receive.

The details of one or more aspects of the disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the disclosure will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a network, in accordance with oneor more aspects of this disclosure.

FIG. 2 is a block diagram illustrating an example of a network interfacedevice in accordance with the techniques described in this disclosure.

FIG. 3 is a block diagram illustrating an example of an optical lineterminal (OLT) in accordance with the techniques described in thisdisclosure.

FIG. 4 is a flowchart illustrating an example method of operation of anOLT in accordance with techniques described in this disclosure.

FIG. 5 is a flowchart illustrating another example method of operationof an OLT in accordance with techniques described in this disclosure.

FIG. 6 is a flowchart illustrating another example method of operationof an OLT in accordance with techniques described in this disclosure.

FIG. 7 is a flowchart illustrating an example method of operation ofnetwork interface device in accordance with techniques described in thisdisclosure.

FIG. 8 is a flowchart illustrating another example method of operationof an OLT in accordance with techniques described in this disclosure.

FIG. 9 is a block diagram illustrating another network, in accordancewith one or more aspects of this disclosure.

FIG. 10 is a flowchart illustrating an example method of operation of anOLT in the network illustrated in FIG. 9.

FIG. 11 is a block diagram illustrating another network, in accordancewith one or more aspects of this disclosure.

FIG. 12 is a flowchart illustrating an example method ofself-quarantining

DETAILED DESCRIPTION

An optical network includes an optical line terminal (OLT), an opticalsplitter/combiner, and a plurality of network interface devices such asoptical network units (ONUs), also referred to as optical networkterminals (ONTs). The OLT connects to the optical splitter/combiner witha fiber link, and each one of the network interface devices connect tothe optical splitter/combiner with respective fiber links. In otherwords, there is a fiber link from OLT to optical splitter/combiner, anda plurality of fiber links (a fiber link for each network interfacedevice) from the optical splitter/combiner to the network interfacedevices.

For downstream transmission, the OLT outputs an optical signal to theoptical splitter/combiner, and the optical splitter/combiner transmitsthe optical signal to each network interface device via respective fiberlinks. Each of the network interface devices determine whether thereceived optical signal is addressed to it or to another networkinterface device. The network interface devices process the opticalsignal when the optical signal is addressed to it.

For upstream transmission, each network interface device transmits arespective optical signal to the optical splitter/combiner, and theoptical splitter/combiner combines the optical signal for transmissionto the OLT. Each network interface device may reside at a subscriberpremises, or a plurality of subscriber premises may share a commonnetwork interface device. Each network interface device receives datafrom devices at one or more subscriber premises, converts the receiveddata into the optical signal, and outputs the optical signal to the OLTvia respective fiber links and the optical splitter/combiner.

To avoid collision of the optical signals from respective networkinterface devices, each network interface device may transmit theoptical signal within an assigned timeslot. For example, the OLT mayassign each of the network interface devices a timeslot within which totransmit respective optical signals, and each network interface devicetransmits its optical signal within the begin and end time of theassigned timeslot. The assigned timeslot is reserved for an upstreamtransmission from a given network interface device.

For example, each network interface device includes a controller, alaser driver, and a laser. The laser driver includes a laser controlinput, which may be a differential input, and based on the laser controlinput causes the laser to output an optical signal or not output anoptical signal (e.g., turn on or turn off the laser based on the lasercontrol input). When the laser is turned on, the laser is able to outputan optical signal including optical ones and optical zeros. When thelaser is turned off, the laser cannot output an optical signal and isessentially dark.

The controller for a given network interface device receives theinformation from the OLT that identifies the timeslot when the networkinterface device is to transmit an optical signal. The controller thenoutputs a voltage (e.g., a digital high) to the laser control input ofthe laser driver to instruct the laser driver to turn on the laser sothat the laser outputs an optical signal during the assigned timeslot(e.g., outputs a digital high at the beginning of the timeslot). Whenthe network interface device is not to transmit an optical signal (e.g.,during non-assigned timeslots or at the conclusion of the timeslot), thecontroller outputs a voltage (e.g., a digital low) to the laser controlinput of the laser driver to instruct the laser driver to turn off thelaser so that the laser does not output an optical signal during thenon-assigned timeslots.

However, in some cases, one or more of the network interface devices maymalfunction and transmit optical signals in timeslots to which thenetwork interface devices are not assigned. As one example, a mechanicalmalfunction at the laser control input may result in the controllerinstructing the laser driver to cause the laser to not output an opticalsignal (e.g., turn off the laser), but the laser driver still causes thelaser to output an optical signal (e.g., keeps the laser turned on). Asanother example, an electrical malfunction within the laser driver mayresult in the laser driver not turning off the laser during anon-assigned timeslot even when the controller outputs a digital lowinstructing the laser driver to turn off the laser. In general, theremay be various causes for why a laser outputs an optical signal atunassigned timeslots.

In the techniques described in this disclosure, a network interfacedevice whose laser is energized (e.g., turned on) outside of the controlof the controller is referred to as a rogue network interface device. Inother words, when the laser is non-responsive to the control of thecontroller, the network interface device is referred to as a roguenetwork interface device. For instance, when a laser is outputting anoptical signal even when the controller is instructing the laser driverto turn off the laser or should be instructing the laser driver to turnoff the laser, the network interface device that includes the controlleris referred to as a rogue network interface device.

In some examples, the rogue network interface device outputs an opticalsignal during a non-assigned timeslot that interferes (e.g., collides)with the optical signal transmitted by another network interface device.In some cases, the rogue network interface device may output an opticalsignal during all timeslots so that the optical signal outputted by therogue network interface device interferes with the optical signals fromeach of the other network interface devices that are properlytransmitting in their own reserved timeslots.

The OLT may be configured to determine whether a rogue network interfacedevice exists in the optical network. As one example, when assigningtimeslots to the network interface devices, the OLT may reserve atimeslot that is not assigned to any of the network interface devices,referred to as a quiet timeslot in this disclosure. For example, whenassigning timeslots, the OLT allocates bandwidth to each of networkinterface devices. Bandwidth that is not allocated to any of the networkinterface devices (e.g., unassigned allocation) may include the quiettimeslot. In this disclosure, the term “unassigned allocation” may alsobe used to refer to the quiet timeslot.

Some rogue network interface devices may always transmit an opticalsignal, and may transmit an optical signal during the reserved timeslotthat is not assigned to any of the network interface devices (e.g.,during the quiet timeslot). In some other techniques, the optical signalmay be noise (e.g., no coherent data) with a certain amount of opticalpower. The OLT may determine whether an optical signal is received inthe quiet timeslot based on the amount of optical power received in thequiet timeslot, and if an optical signal is received in the quiettimeslot, determines that a rogue network interface device exists in theoptical network.

While the OLT may determine that a rogue network interface device existsin the optical network, it may be unknown which network interface deviceis the rogue network interface device. This disclosure describesexamples ways to determine which network interface device is the roguenetwork interface device. As described in more detail, the controller ofeach network interface device may be configured to instruct the laserdriver to turn off the laser during the non-assigned timeslot, but alsooutput a predefined data pattern to the laser driver during thenon-assigned timeslot. For the properly functioning network interfacedevices, the predefined data pattern will not propagate as an opticalsignal because the laser is off and under control of the controller.However, for the rogue network interface device, the predefined datapattern will propagate as an optical signal because the laser is on(when it should be off) and not under control of the controller.

The OLT may determine which network interface device is the roguenetwork interface device based on the optical signal received in thequiet timeslot. As one example, the predefined data pattern may be aunique identifier of the network interface device used for rogue networkinterface device identification, where each controller outputs adifferent, unique data pattern. The unique data pattern serves as aunique identifier that identifies a respective network interface device.In this example, the OLT may determine which network interface device isthe rogue network interface device based on the unique identifierembedded in the optical signal received in the quiet timeslot.

As another example, the OLT may utilize two different predefined datapatterns (e.g., a first predefined data pattern and a second predefineddata pattern used for rogue network interface device identification).The first predefined data pattern may have a first transitional density(e.g., a ratio of the number of ones to zeros in the data pattern). Thisdata pattern may be the same for each of the network interface devices,or the transitional density may be the same even if the pattern isdifferent. The second predefined data pattern may be the same for eachcontroller, and may have a second, different transitional density thanthe first transitional density.

In this example, the OLT may instruct each of the network interfacedevices to output the first predefined data pattern during timeslots towhich the network interface devices are not assigned. The OLT may thendetermine the transitional density of the optical signal received duringthe quiet timeslot. Again, for the properly functioning networkinterface devices, the first predefined data pattern will not propagateas an optical signal because their lasers are off, but the firstpredefined data pattern will propagate as an optical signal from therogue network interface device because its laser is turned on, eventhough it should be turned off.

Then, the OLT may perform a linear search to identify the rogue networkinterface device. For example, the OLT may instruct the first networkinterface device to switch from the first predefined data pattern to thesecond predefined data pattern, but may not instruct any of the othernetwork interface devices to switch. Instead, the other networkinterface devices may continue to transmit the first predefined datapattern. The OLT may then determine the transitional density receivedduring the quiet timeslot. In this example, the controller of the firstnetwork interface device outputs the second predefined data pattern tothe laser driver during timeslots to which the first network interfacedevice is not assigned.

If the first network interface device were the rogue network interfacedevice, then the transitional density of the optical signal in the quiettimeslot would be different, as compared to when the OLT received thefirst predefined data pattern propagated as an optical signal in thequiet timeslot. Because the first network interface device, as a roguedevice, is transmitting in the quiet timeslot, when it should not betransmitting, a change in the transitional density of the first andsecond predefined data patterns generated by the first network interfacedevice can be detected. In this case, the OLT may determine that thefirst network interface device is the rogue network interface device.

If the first network interface device were not the rogue networkinterface device, then the transitional density of the optical signal inthe quiet timeslot would be the same as when the OLT received the firstpredefined data pattern propagated as an optical signal in the quiettimeslot. The reason for this is that only the first network interfacedevice switched from the first predefined data pattern to the secondpredefined data pattern. Therefore, if the transitional density in thequiet timeslot did not change, one of the other network interfacedevices is transmitting the first predefined data pattern in the quiettimeslot.

If the OLT determines that the first network interface device is not therogue network interface device, the OLT may cause the second networkinterface to switch from the first predefined data pattern to the secondpredefined data pattern and repeat the above techniques described withrespect to the first network interface device. The OLT may repeat thesetechniques until the OLT eliminates from consideration the non-roguenetwork interface devices and thereby identifies the rogue networkinterface device.

In the above examples, the controllers of the network interface devicesare configured to output the predefined data pattern (e.g., the uniqueidentifier or first or second data patterns with different transitionaldensity) during timeslots that are not assigned to the network interfacedevices. During timeslots assigned to a network interface device, thenetwork interface device may convert the data received from the devicesat the one or more subscriber premises into an optical signal and outputthe optical signal.

For example, if a first network interface device is not a rogue networkinterface device, during timeslots not assigned to the first networkinterface device, the controller of the first network interface deviceoutputs a predefined data pattern (as described above) to the laserdriver, but this predefined data pattern does not get converted to anoptical signal because the laser is turned off During timeslots assignedto the first network interface device, the controller of the firstnetwork interface device outputs the data received from devices at theone or more subscriber premises that use the first network interfacedevice for upstream transmission, converts the data into an opticalsignal, and outputs the optical signal.

If a second network interface device is a rogue network interfacedevice, during timeslots not assigned to the second interface device,the controller of the second network interface device outputs apredefined data pattern (as described above) to the laser driver, andthis predefined data pattern gets converted to an optical signal andoutputted because the laser is turned on even though it should be turnedoff During timeslots assigned to the second network interface device,the controller of the second network interface device outputs the datareceived from devices at the one or more subscriber premises that usethe second network interface device for upstream transmission, convertsthe data into an optical signal, and outputs the optical signal.

In this manner, the techniques allow for rogue network interface devicedetection without needing to disable the upstream data transmission fromthe network interface devices. For instance, it may be possible todisable the upstream data transmission of each of the network interfacedevices upon detection of a rogue network interface device. Then, theOLT turns on each network interface device one at a time and determineswhether an optical signal exists in the quiet timeslot to identify therogue network interface device. However, such techniques requireinterrupting the transmission of upstream data until the rogue networkinterface device is identified. Such interruption of transmissionnegatively impacts the performance of the optical network (e.g., thesubscriber devices cannot transmit upstream data for an extended periodof time). With the techniques described in this disclosure, suchinterruption of transmission may not be needed. For instance, in someexamples, if the techniques described in this disclosure are not able toaccurately identify the rogue network interface device are thetechniques of sequentially disabling network interface devices employed.

Disabling upstream transmission of a network interface device should notbe confused as turning off the laser during timeslots not assigned to anetwork interface device. For instance, disabling upstream transmissionof a network interface device is a hard shutdown of the upstreamtransmission such as by disabling power to the laser driver or thelaser. When the laser is turned off or attempted to be turned off duringtimeslots not assigned to a network interface device, the laser driveris controlling the current flowing through the laser to be very small.In this way, it may still be possible to disable upstream transmissionof a rogue network interface device even if the controller is unable tocontrol when the laser is to turn off.

Some other techniques have also been proposed to identify the roguenetwork interface device without needing to disable the networkinterface devices. These other techniques store a look-up table of theoptical power delivered by each of the network interface devices,measure the optical power of the optical signal received in the quiettimeslot, and compare the measured optical power to the optical powerdelivered by each of the network interface devices to identify the roguenetwork interface device. In these other techniques that rely on opticalpower, the optical signal received in the quiet timeslot is a noisyoptical signal, meaning that there is no discernible or recoverable datapattern embedded in the optical signal, but instead includes randomoptical ones and zeros over the entire frequency range.

However, relying on optical power to identify the rogue networkinterface device may not function well. For instance, many of thenetwork interface devices may deliver approximately the same amount ofoptical power, and determining which one of these network interfacedevices is the rogue network interface device may still requiredisabling upstream transmission, albeit for a smaller set of networkinterface devices. Also, the OLT may include an optical interface module(OIM) circuitry that includes a signal strength meter to detect theinstantaneous optical power (e.g., real-time). However, the OIMdetection circuitry, from which the signal strength is determined, maybe fairly imprecise, with a relatively large margin of error.Furthermore, while handheld optical meters may be fairly precise, thesehandheld optical meters measure an average of the optical power (e.g.,not real-time), when instantaneous power measurements are needed, andrequire disconnection of the fiber link for connection with the opticalmeter. Accordingly, in these other techniques, it may be difficult todetermine which network interface device is the rogue network interfacedevice because power measurement may not be precise, or otherwiseimpractical to obtain, making it difficult to distinguish betweendifferent network interface devices.

The above examples may be extended to multiple wavelength systems. Anexample of a multiple wavelength system is the ITU-T G.989 (NGPON-2)standard. In a multiple wavelength system, there may exist a pluralityof OLTs (e.g., at different geographical locations, different OLT cardswithin the same chassis, or other configurations with multiple OLTs). Insome examples of the multiple wavelength system, there may be one OLTthat is configured to transmit and receive optical signals via multipledifferent wavelengths. For ease of illustration, the examples aredescribed with respect to there being multiple OLTs in a multiplewavelength system.

In a multiple wavelength system, each OLT of a plurality of OLTs isassociated with a set of all network interface devices and communicates(e.g., transmits and receives) only with the network interface deviceswithin the associated set. For example, in the multiple wavelengthsystem, a first OLT is associated with a first set (e.g., group) of oneor more network interface devices and communicates with the one or morenetwork interface devices that belong to the first set. In the multiplewavelength system, a second OLT is associated with a second set ofdifferent one or more network interface devices and communicates withthe one or more network interface devices that belong to the second set,and so forth. After initialization and assignment of network interfacedevices to OLTs, an OLT may not be able to transmit downstream opticalsignals to a network interface device to which it is not associated. Ingeneral, after initialization and assignment of network interfacedevices to OLTs, a network interface device should not transmit upstreamoptical signals to an OLT to which it is not associated.

To effectuate such communication, each OLT may be assigned differentupstream/downstream wavelength pairs, and each set of network interfacedevices may be assigned different upstream/downstream wavelength pairsrelative to the other sets of network interface devices. As an example,a first OLT may be configured to transmit downstream optical signals ata first downstream wavelength, and receive upstream optical signals at afirst upstream wavelength. The first set of network interface devices,associated with the first OLT, may be configured to receive downstreamoptical signals at the first downstream wavelength, and transmitupstream optical signals at the first upstream wavelength.

A second OLT may be configured to transmit downstream optical signals ata second downstream wavelength, and receive upstream optical signals ata second upstream wavelength. The second set of network interfacedevices, associated with the second OLT, may be configured to receivedownstream optical signals at the second downstream wavelength, andtransmit upstream optical signals at the second upstream wavelength, andso forth. In this example, each of the wavelengths is different than theothers. For instance, the first downstream wavelength is different thanthe second downstream wavelength, the first upstream wavelength, and thesecond upstream wavelength, and the same is true for the seconddownstream wavelength, the first upstream wavelength, and the secondupstream wavelength.

In some examples, in a multiple wavelength system, a network interfacedevice in a first set of network interface devices may become rogue(e.g., transmit upstream optical signals during one or more timeslots towhich it is not assigned). In this example, the first OLT may be able toidentify which network interface device in the first set of networkinterface devices is rogue using the example techniques described above.

However, in some cases, in addition to becoming rogue, a networkinterface device may also transmit upstream optical signals at awavelength to which it is not assigned. For instance, the networkinterface devices may be tunable to distinct upstream and downstreamwavelengths, and may be tuned to transmit and receive optical signals atthe assigned upstream and downstream wavelengths, respectively. However,external factors or some other error may cause a network interfacedevice to become un-tuned and begin transmitting upstream opticalsignals at a different wavelength.

For example, a network interface device in a first set may begin totransmit upstream optical signals at an upstream wavelength assigned tonetwork interface devices in a second set. In this example, the firstOLT may not receive the upstream optical signals from this networkinterface device in the first set, and instead, the second OLT mayreceive the upstream optical signals from this network interface devicein the first set.

In some examples, if a network interface device becomes rogue andtransmits upstream optical signals at an upstream wavelength to which itis not assigned, an OLT, other than the OLT to which the networkinterface device is assigned, will receive the optical signal the quiettimeslot. In this case, the OLT will receive optical signals in thequiet timeslot, and determine that a rogue network interface deviceexists. However, because the rogue network interface device is not anetwork interface device associated with (e.g., assigned to) the OLTthat determined that a rogue network interface device exists, the OLTmay not be able to quarantine the rogue network interface device orcause the rogue network interface device to switch between predefineddata patterns.

In accordance with the techniques described in this disclosure, for themultiple wavelength system, each of the OLTs may be configured totransmit and receive data from one another in an out of bandcommunication. In these examples, the OLT that determined that a roguenetwork interface device exists is referred to as a detector OLT, andthe OLT that is able to communicate with the rogue network interfacedevice is referred to as a controller OLT. For instance, if the roguenetwork interface device is transmitting upstream optical signals to theOLT with which it is associated (e.g., to which it is assigned), thenthe detector OLT and the controller OLT are the same OLT. However, ifthe rogue network interface device is transmitting upstream opticalsignals with which it is not associated, then the detector OLT becomesthe OLT that receives the optical signals from the rogue networkinterface device, and the controller OLT becomes the OLT with which thenetwork interface device is associated. The detector OLT and thecontroller OLT may together identify the rogue network interface device.

For instance, in the example where the controllers of the networkinterface devices are configured to transmit a unique identifier duringone or more timeslots to which the network interface devices are notassigned, the detector OLT may determine (e.g., reconstruct) the uniqueidentifier from the optical signal received in the quiet timeslot. Thedetector OLT may determine whether the unique identifier is for anetwork interface device with which the OLT is associated. If thedetector OLT determines that the unique identifier is for a networkinterface device with which the OLT is associated, the detector OLT mayquarantine the rogue network interface device.

If the detector OLT determines that the unique identifier is for anetwork interface device with which the OLT is not associated, in oneexample, the detector OLT may determine with which OLT the rogue networkinterface device is associated (e.g., which is the controller OLT). Forinstance, each OLT may store a look up table that identifies all of thenetwork interface devices associated with respective OLTs, and thedetector OLT may determine with which OLT the rogue network interfacedevice is associated based on the look up table (e.g., determine thecontroller OLT for the rogue network interface device). The detector OLTmay then indicate to the determined controller OLT that the networkinterface device identified by the reconstructed unique identifier isrogue.

In some examples, instead of or in addition to determining thecontroller OLT, the detector OLT may broadcast a signal to each of theother OLTs that includes the unique identifier of the rogue networkinterface device and that requests that the OLT associated with therogue network interface device disable the rogue network interfacedevice. In this example, each of the OLTs that received the signal maydetermine whether it is the controller for the rogue network interfacedevice.

As described above, in some examples, rather than using a uniqueidentifier or if using the unique identifier is not successful, an OLTmay request for each controller of each of the network interface devicesto transmit a signal with a first transitional density during one ormore timeslots to which the network interface devices are not assigned.The OLT may determine the transition density of the received opticalsignal in the quiet timeslot, and then instruct each controller of eachnetwork interface device to transmit a signal with a second transitionaldensity, one at a time, during timeslots to which the network interfacedevices are not assigned. Based on when there is a change in thetransition density of the optical signal received in the quiet timeslot,the OLT may determine which network interface device is the roguenetwork interface device.

In the context of multiple wavelength system, the detector OLT mayinstruct each of the other OLTs to instruct each of the controllers oftheir network interface devices to transmit signals with the firsttransitional density. The detector OLT may determine the transitiondensity of the optical signal received in the quiet timeslot. Thedetector OLT may then request a first OLT to instruct a controller of afirst network interface device associated with the first OLT to switchfrom the signal with the first transitional density to the signal withthe second transitional density. The detector OLT may then determinewhether there was a change in the transition density of the opticalsignal received in the quiet timeslot. If there is change in thetransition density, the detector OLT may determine that the firstnetwork interface device of the first OLT is the rogue network interfacedevice. If there is no change in the transition density, the detectorOLT may request the first OLT to instruct a controller for a secondnetwork interface device associated with the first OLT to switch fromthe signal with the first transitional density to the signal with thesecond transitional density.

The detector OLT may repeat these steps until the rogue networkinterface device is identified, or until the controllers of all networkinterface devices associated with the first OLT have transmitted thesignal with the second transitional density. If the controllers of allnetwork interface devices associated with the first OLT have transmittedthe signal with the second transitional density, and there has been nochange in the transition density of the optical signal received in thequiet timeslot by the detector OLT, then the detector OLT may requestthe second OLT to instruct the controller of the first network interfacedevice associated with the second OLT to transmit the optical signalwith the second transition density, and so forth, until the transitiondensity of the optical signal received in the quiet timeslot of thedetector OLT changes.

In this manner, it may be possible to identify the rogue networkinterface device in the multiple wavelength system. For example, thedetector OLT may receive a data pattern in an optical signal receivedfrom one of a plurality of network interface devices with which thedetector OLT is not configured to communicate in a quiet timeslot. Thedetector OLT may communicate (e.g., interface) with one or more otherOLTs (e.g., one or more controller OLTs) for determining which one ofthe network interface devices transmitted the optical signal during thequiet timeslot based on the data pattern to identify a rogue networkinterface device.

In the above examples, a rogue network interface device transmitsoptical signals at timeslots to which it is not assigned. However, insome cases, a network interface device may be transmitting opticalsignals at timeslots to which it is assigned, but its laser may becomeun-tuned. The laser becoming un-tuned may cause the laser to transmitthe optical signal to an OLT to which the network interface device isnot associated. In some examples, the OLT associated with the networkinterface device may transmit a request to the network interface deviceto confirm whether the network interface device is transmitting opticalsignals during timeslots assigned to the network interface devices. Inresponse to receiving the request, the network interface device maydetermine whether the network interface device is transmitting opticalsignals during its assigned timeslots. If the network interface devicedetermined that it is transmitting optical signals during its assignedtimeslots, but received the request from the OLT to which it isassociated, the network interface device may determine that its laser isnot transmitting at the correct wavelength. In such examples, inresponse, the network interface device may disable the upstreamtransmission.

FIG. 1 is a block diagram illustrating a network 10. For purposes ofillustration, the example implementations described in this disclosureare described in context of an optical network (e.g., a passive opticalnetwork (PON)). Accordingly, network 10 may be referred to as PON 10.However, aspects of this disclosure are not so limited, and can beextended to other types of networks such as cable or digital subscriberline (DSL) based networks, or Active Ethernet which may be considered asoptical transmission and reception in accordance with the Ethernetprotocol. Active Ethernet is defined by the IEEE 802.3ah standard (e.g.,in clause 59 of the 802.3ah standard). Examples of network 10 alsoinclude shared-medium transports such as WiFi and RF/DOCSIS.

As shown in FIG. 1, PON 10 may deliver voice, data and video content(generally “information”) to a number of network nodes via optical fiberlinks. In some examples, PON 10 may be arranged to deliver InternetProtocol television (IPTV) and other high speed information (e.g.,information transmitted at approximately 200 Mbps or higher). PON 10 mayconform to any of a variety of PON standards, such as the broadband PON(BPON) standard (ITU G.983), Ethernet PON (EPON), the gigabit-capablePON (GPON) standard (ITU G.984), or 10 giga-bit NGPON, as well as futurePON standards under development by the Full Service Access Network(FSAN) Group, such as 10G GPON (ITU G.987), or other organizations.

Optical line terminal (OLT) 12 may receive voice information, forexample, from the public switched telephone network (PSTN) 14 via aswitch facility 16. In addition, OLT 12 may be coupled to one or moreInternet service providers (ISPs) 18 via the Internet and a router 20.As further shown in FIG. 1, OLT 12 may receive video content 22 fromvideo content suppliers via a streaming video headend 24. Video also maybe provided as packet video over the Internet. In each case, OLT 12receives the information, and distributes it along optical fiber link 13to optical splitter/combiner 26.

Optical splitter/combiner 26 then distributes the information to networkinterface devices 28A-28N (collectively referred to as “networkinterface devices 28”) via respective fiber optic links 27A-27N(collectively referred to as “fiber optic links 27”). In some examples,PON 10 includes 128 network interface devices 28; however, the aspectsof this disclosure are not so limited. Also, network interface devices28 may be referred to as optical network units (ONUs) or optical networkterminals (ONTs).

A single network interface device 28 is an example of a networkinterface device. Other examples of a network interface device include,but are not limited to, a cable modem or a DSL modem. However, forpurposes of illustration but without limitation, the exampleimplementations described in the disclosure are described in the contextof the network interface device being an ONU or ONT.

Each one of network interface devices 28 may reside at or near asubscriber premises that includes one or more subscriber devices 30A-30N(collectively referred to as “subscriber devices 30”). For instance,network interface device 28A resides at or near a subscriber premisesthat includes one or more subscriber devices 30A, and network interfacedevice 28N resides at or near a subscriber premises that includes one ormore subscriber devices 30N. The subscriber premises may be a home, abusiness, a school, or the like. A single network interface device 28may be capable of transmitting information to and receiving informationfrom one or more subscriber premises.

As illustrated, a single network interface device 28 may directlytransmit information to or receive information from one or moresubscriber devices 30 within the subscriber premises. Examples of thesubscriber devices 30 include, but are not limited to, one or morecomputers (e.g., laptop and desktop computers), network appliances,televisions, game consoles, set-top boxes, wireless devices, mediaplayers or the like, for video and data services, and one or moretelephones for voice services. Subscriber devices 30 may also includehousehold appliances such as furnaces, washer and dryers, freezers,refrigerators, thermostats, lights, security systems, and the like.

OLT 12 transmits downstream information to and receives upstreaminformation from network interface devices 28 via fiber link 13 coupledto splitter/combiner 26. Downstream information may be considered to beinformation transmitted by OLT 12 and received by network interfacedevices 28. Upstream information may be considered to be informationtransmitted by each one of network interface devices 28 and received byOLT 12. As illustrated in FIG. 1, optical splitter/combiner 26 may becoupled to each one of network interface devices 28 via respectiveoptical fiber links 27.

In some examples, optical splitter/combiner 26 may be a passivesplitter/combiner. A passive splitter/combiner may not need to bepowered. For downstream transmission, including voice, video, and datainformation from OLT 12, optical splitter/combiner 26 receives thedownstream information and splits the downstream information fordownstream transmission to network interface devices 28 via respectivefiber links 27. For upstream information, including voice and datainformation from each one of network interface devices 28, opticalsplitter/combiner 26 receives upstream information from networkinterface devices 28 via respective fiber links 27 and combines theupstream information for transmission to OLT 12.

In some examples, optical splitter/combiner 26 may not be a passivesplitter/combiner, but rather an active splitter/combiner. In theseexamples, optical splitter/combiner 26 may be powered locally. In theseexamples, optical splitter/combiner 26 may function as a switch, router,multiplexer, and the like.

Network interface devices 28 receive and transmit information viarespective fiber links 27. Also, OLT 12 receives and transmitsinformation via fiber link 13. To differentiate between transmission andreception, each one of network interface devices 28 may be configured totransmit voice and data information with an optical signal with awavelength of 1310 nanometer (nm), receive voice and data informationwith an optical signal with a wavelength of 1490 nm, and receive videoinformation with an optical signal with a wavelength of 1550 nm. OLT 12may be configured to receive voice and data information with an opticalsignal with a wavelength of 1310 nm, transmit voice and data informationwith an optical signal with a wavelength of 1490 nm, and transmit videoinformation with an optical signal with a wavelength of 1550 nm. Thesewavelengths are provided merely as examples.

The specific transmit and receive wavelengths indicated above areprovided for illustration purposes only. In different examples, networkinterface devices 28 and OLT 12 may be configured to transmit andreceive information with optical signals at different wavelengths thanthose provided above. However, the transmission and receptionwavelengths of the optical signals should be different.

Each one of network interface devices 28 may be configured to transmitupstream information according to time division multiple access (TDMA)techniques. For instance, OLT 12 may grant or assign to each ofsubscriber devices 30 certain timeslots during which to transmitupstream information. Each one of network interface devices 28 transmitsinformation to OLT 12 based on the timeslots assigned to each ofrespective subscriber devices 30. The timeslot for each one networkinterface devices 28 may be different. In this manner, each one ofnetwork interface devices 28 may transmit information without collisionof information from two or more different network interface devices 28at splitter/combiner 26. Collision of information may occur ifsplitter/combiner 26 receives upstream information from two or morenetwork interface devices 28 at the same time.

As one example of the TDMA techniques, when one of network interfacedevices 28 (e.g., network interface device 28A), is powered on for thefirst time, OLT 12 may perform an auto-ranging process, as is well knownin the art. For instance, during the auto-ranging process, OLT 12 maycalculate the total propagation delay (e.g., the total time it takes totransmit information to network interface device 28A and receiveinformation from network interface device 28A). OLT 12 may performsimilar auto-ranging process on each one of network interface devices28.

After the auto-ranging process, OLT 12 may calculate an equalizationdelay for each one of network interface devices 28, utilizing techniqueswell known in the art. The equalization delay equalizes the propagationdelay of each one of network interface devices 28, relative to the othernetwork interface devices 28. OLT 12 may transmit the equalization delayto each one of network interface devices 28 utilizing a physical layeroperations and maintenance (PLOAM) message or utilizing an ONUmanagement control interface (OMCI) message.

Once all the equalization delays are calculated and transmitted tonetwork interface devices 28, OLT 12 may grant the timeslots duringwhich each one of network interface devices 28 should transmit data(e.g., an optical signal). OLT 12 may transmit a bandwidth map to eachone of network interface devices 28 indicating the timeslots duringwhich each one network interface devices 28 should transmit data. OLT 12may transmit the bandwidth map utilizing a PLOAM or OMCI message, orother message. In this way, PON 10 utilizes time division multiplexingto precisely synchronize transmission from all ONTs (e.g., networkinterface devices 28) such that each ONT transmits during a window whereall other ONTs are quiet.

However, because PON 10 is a shared medium for network interface devices28, PON 10 may be susceptible to network outages due to a singlemisbehaved (e.g., malfunctioning) network interface device 28. Forexample, although each one of network interface devices 28 should outputan optical signal representing the data received from subscriber devices30 during its assigned timeslot, a malfunctioning network interfacedevice 28 may transmit an optical during a timeslot to which it is notassigned.

For instance, each one of network interface devices 28 includes acontroller, such as a media access control (MAC) controller, thatinstructs a laser driver to turn on the laser (e.g., energize the laser)during its assigned timeslot and to turn off the laser (e.g.,de-energize the laser) during timeslots to which it is not assigned. Inthe techniques described in this disclosure, one of network interfacedevices 28 whose laser becomes energized outside the control of itscontroller is referred to as a rogue network interface device. Forexample, if the controller instructs the laser driver to turn off thelaser, but the laser does not turn off, the laser may be considered asbeing energized outside the control of its controller (e.g., the laserdriver is non-responsive to the instructions from the controller to turnoff the laser).

The existence of a rogue network interface device in PON 10 may be asignificant failure mode of PON 10. For example, the optical signaltransmission from the rogue network interface device falls outside theallowed timeslots and is sent coincidently with the proper transmissionfrom other ones of network interface devices 28. For example, networkinterface device 28A may be assigned a first timeslot in which totransmit an optical signal, and network interface device 28N may beassigned a second timeslot in which to transmit an optical signal. Ifnetwork interface device 28A were a rogue network interface device,network interface device 28A may transmit an optical signal during thefirst timeslot, which will be data from subscriber devices 30A. Inaddition, network interface device 28A may transmit an optical signalduring the second timeslot which coincides, and hence collides, with theoptical signal of network interface device 28N, which will be data fromsubscriber devices 30N.

In this case, the optical signal outputted by network interface device28A during the second timeslot (e.g., the timeslot to which networkinterface device 28A is not assigned) may be a noisy optical signal withrandom optical ones and zeros and not at a fixed data rate. This noisyoptical signal from network interface device 28A mixes with opticalsignal from network interface device 28N in the second timeslotresulting in the inability of OLT 12 to properly reconstruct the datatransmitted by subscriber devices 30N via network interface device 28Nin the second timeslot (e.g., causing recovery issues at OLT 12). Forexample, there may be a significant number of bit-errors in thereconstructed data transmitted by subscriber devices 30N via networkinterface device 28N in the second timeslot.

In a point-to-point network, an uncontrolled laser of a rogue networkinterface device may only affect the rogue network interface device.However, in PON 10, an uncontrolled laser of a rogue network interfacedevice may affect one or more of the other network interface devices 28.For example, if the laser of the rogue network interface device isalways energized, then the rogue network interface device may output anoptical signal in all of the timeslots, which will cause the opticalsignal of the rogue network interface device to collide with the opticalsignals from all other network interface devices 28. As described above,PON 10 may include 128 network interface devices 28, and it may bepossible for the rogue network interface device to corrupt the upstreamtransmissions from all 127 other network interface devices 28.

OLT 12 may be configured to detect the existence of a rogue networkinterface device in PON 10. As one example way, in assigning each one ofnetwork interface devices 28 an upstream transmission timeslot, OLT 12may reserve one timeslot that is not assigned to any of networkinterface devices 28, referred to as a quiet timeslot. For example,bandwidth not allocated to any of the network interface devices 28 mayinclude the quiet timeslot. Accordingly, the term “unassignedallocation” may also refer to the quiet timeslot. If no rogue networkinterface device exists in PON 10, then there would be no optical signalduring the quiet timeslot. If a rogue network interface device exists inPON 10, then there would be an optical signal during the quiet timeslot.

OLT 12 may be configured to determine whether OLT 12 received an opticalsignal during the quiet timeslot. If OLT 12 determines that an opticalsignal was received in the quiet timeslot, then OLT 12 determines that arogue network interface device exists in PON 10. There may be other waysin which to determine the existence of a rogue network interface device,and the techniques described in this disclosure are not limited to anyspecific technique for determining the existence of the rogue networkinterface device.

While OLT 12 may determine that a rogue network interface device exists,OLT 12 may not be able to determine (e.g., identify) which one ofnetwork interface devices 28 is the rogue network interface device. Thisdisclosure describes example techniques for identifying a rogue networkinterface device.

The disclosure describes an example of using self-identifying backgroundpatterns for rogue network interface device identification (referred toas the “self-identifying background patterns technique”). The disclosurealso describes an example of using differential pattern transitiondensity for rogue network interface device identification (referred toas the “differential pattern transition technique”). These exampletechniques may be used together or separately. For instance, in someexamples, PON 10 may implement the self-identifying background patternstechnique to identify the rogue network interface device, and may notimplement the differential pattern transition density technique toidentify the rogue network interface device. In some examples, PON 10may implement the differential pattern transition density technique toidentify the rogue network interface device, and may not implement theself-identifying background patterns technique to identify the roguenetwork interface device.

In some examples, PON 10 may implement the self-identifying backgroundpatterns technique to identify the rogue network interface device in afirst phase, and if unsuccessful in identifying the rogue networkinterface device, implement the differential pattern transition densitytechnique, or vice-versa. In examples where PON 10 implements theself-identifying background patterns technique and/or the differentialpattern transition density technique, it may be possible for thetechnique(s) to be unsuccessful in identifying the rogue networkinterface device. In some examples, if one or both of the techniques areunable to identify the rogue network interface device, PON 10 may relyupon conventional techniques for rogue network interface detection.

However, identifying the rogue network interface device utilizingtechniques described in the disclosure may provide advantages overidentifying the rogue network interface device utilizing conventionaltechniques. The techniques described in this disclosure, including theself-identifying background patterns technique and the differentialpattern transition density technique, cause controllers of networkinterface devices 28 to transmit to respective laser drivers apredefined data pattern during timeslots to which it is not assigned.

For properly functioning network interface devices 28 (e.g., non-roguenetwork interface devices 28), this predefined data pattern will not beconverted to an optical signal because the laser will be turned off, asinstructed by the controller. For the rogue network interface device,this predefined data pattern will be converted to an optical signalbecause the laser will be on, contrary to the instructions from thecontroller.

OLT 12 may receive an optical signal embedded with the predefined datapattern during the timeslot not assigned to any of network interfacedevices 28 (i.e., the quiet timeslot). For instance, because none ofnetwork interface devices 28 are to output an optical signal during thequiet timeslot, only the rogue network interface device may output anoptical signal during the quiet timeslot. OLT 12 may then determinewhich one of network interface devices 28 is rogue (e.g., identify therogue network interface device) by sampling the optical signal in quiettimeslot and recovering the predefined data pattern.

In the techniques described in this disclosure, during assignedtimeslots, network interface devices 28 output optical signals based onthe data received from subscriber devices 30. During all timeslots towhich one of network interface devices 28 is not assigned, one ofnetwork interface devices 28 may output a predefined data pattern usedfor rogue network interface device identification. The other networkinterface devices 28 may function in a similar way. To avoid confusionwith the data pattern that network interface devices 28 output duringassigned timeslots, this disclosure may at times use the term“background pattern” or “off-pattern” to refer to the data pattern thateach one of network interface devices 28 outputs during timeslots towhich it is not assigned for rogue network interface deviceidentification.

As an example, the controller of network interface device 28A may outputthe data pattern received from subscriber devices 30A during thetimeslot assigned to network interface device 28A. During timeslots notassigned to network interface device 28A, the controller of networkinterface device 28A may output a background pattern (e.g., a predefineddata pattern). Network interface devices 28B-28N may function in asimilar manner, except their controllers output the data patternreceived from respective subscriber devices 30B-30N.

In other words, in some examples, the controllers of network interfacedevices 28 may output a serialized data pattern independent of whetherthe laser is on or off. However, if the controller instructs the laserto be on, the controller may output the data received from respectivesubscriber devices 30. If the controller instructs the laser to be off,the controller may output the background or off-pattern (e.g., apredefined data pattern).

In some examples, the controllers of network interface devices 28 mayalready be configured to output background or off-patterns to respectivelaser drivers even when the controllers instructs the laser driver toturn off the laser (e.g., burst enable is in an off state, as describedmore below) to support calibration patterns during manufacturing. Forinstance, even if a controller instructs the laser driver to turn offthe laser, the transmit data lines between the controller and the laserdriver are active. In examples where the controllers are alreadyconfigured to output background or off-patterns, these background oroff-patterns may be programmable and/or selectable. In some examples,the background or off-patterns may be a pattern of all digital zerossince no valid data is being transmitted.

However, in the techniques described in this disclosure, the controlleroutputs a predefined data pattern as the background or off-pattern(e.g., rather than transmitting a pattern of all digital zeros). In someexamples, the controllers may be configured to always or periodicallyoutput the predefined data pattern as the background pattern. In someexamples, the controllers may be configured to output the predefineddata pattern as the background pattern in response to OLT 12 indicatingthat a rogue network interface device exists. For instance, aproprietary physical layer operations, administration, and maintenance(PLOAM) message has been created per the G.984.3 standard to control thebackground pattern of network interface devices 28 (e.g., of the ONUs).If rogue detection is enabled, OLT 12 may send this PLOAM to all networkinterface devices 28 to turn on detectable background patterns. If roguedetection is disabled, OLT 12 may program network interface devices 28to have a zero-pattern background since this is the least destructivepattern and well-suited when no rogue detection is enabled.

In the self-identifying background pattern technique, the predefineddata pattern is different for each of network interface devices 28, andthe predefined data pattern for one of network interface devices 28functions as a unique identifier for that one of network interfacedevices 28 (e.g., as an ONU-ID). In some examples, the controller may bepreprogrammed with the unique identifier for the one of networkinterface devices 28 to which the controller will belong. In someexamples, OLT 12 may assign each one of network interface devices 28with a unique identifier that the respective controllers store. Theremay be other ways in which network interface devices 28 are assignedunique identifiers, and the techniques described in this disclosure arenot limited to any particular technique to assign unique identifiers tonetwork interface devices 28.

In this example, the rogue network interface device will transmit itsunique identifier as the predefined data pattern during timeslots towhich the rogue network interface device is not assigned. OLT 12 mayreceive this unique identifier in the quiet timeslot as embedded in theoptical signal, and OLT 12 may sample the optical signal to reconstructthe unique identifier. OLT 12 may then identify the rogue networkinterface device based on the reconstructed unique identifier. In otherwords, by programming a unique value into the background pattern that isrelated to the ONU-ID, OLT 12 can monitor for rogue power (e.g., powerin the quiet timeslot) and sample the pattern to determine the ONU-ID ofthe rogue network interface device.

In other words, OLT 12 may receive a data pattern, embedded with aunique identifier, from an optical signal received during a quiettimeslot. As described above, the quiet timeslot is a timeslot that isnot allocated to any of the plurality of network interface devices 28for upstream transmission (i.e., none of network interface devices 28 isto transmit an optical signal during the quiet timeslot). OLT 12 mayidentify a rogue network interface device from the plurality of networkinterface devices 28 as one of the network interface devices having aunique identifier that is same as the unique identifier embedded in thedata pattern received during the quiet timeslot.

In some examples, for confirmation that the identified network interfacedevice truly is a rogue network interface device, OLT 12 may sample theoptical signal in the quiet timeslot for multiple instances of the quiettimeslot. If the same network interface device is identified in theoptical signals in each of the multiple instances of the quiet timeslot,OLT 12 may confirm that the identified network interface device is therogue network interface device.

For example, assume that network interface device 28N is the roguenetwork interface device. In this example, during the first timeslot,network interface device 28A will output data from subscriber devices30A, and network interface device 28N will output its unique identifier.During the second timeslot, network interface device 28N will outputdata from subscriber devices 30N. During the quiet timeslot, networkinterface device 28N will output its unique identifier (e.g., outputs anoptical signal that includes the unique identifier). OLT 12 reconstructsthe unique identifier from the optical signal and determines (e.g.,identifies) network interface device 28N as the rogue network interfacedevice based on the unique identifier. For instance, OLT 12 may identifynetwork interface device 28N as the rogue network interface devicebecause network interface device 28N has the same unique identifier asthe unique identifier embedded in the data pattern received during thequiet timeslot. In some examples, OLT 12 may reconstruct the uniqueidentifier in the quiet timeslot multiple times to confirm that networkinterface device 28N is the rogue network interface device. In otherwords, depending on the acceptable error rate, continuous sequentialevents may be advisable to eliminate false matches due to networkinterface devices 28 that are sending random data.

In some examples, the predefined data patterns that each includesembedded unique identifiers for network interface devices 28 may includethe following example properties. These properties are provided forpurposes of illustration only and should not be considered limiting.

As one example, the one/zero duty cycle of the data pattern of a uniqueidentifier may be in the range of approximately 40% to 60%. The laserdriver of each of network interface devices 28 may include an automaticpower control (APC) loop that controls the amplitude of the current(e.g., bias current and/or modulation current) delivered to the laser.The APC loop may require sufficient data transitions in the data patternto function properly. By having a duty cycle in the range ofapproximately 40% to 60%, there may be sufficient data transitions forthe APC loop to function properly.

As another example, to indicate the end of the unique identifier withinthe predefined data pattern, the predefined data pattern of each ofnetwork interface devices 28 may include a framing delimiter, such as a24-bit framing delimiter. Although the unique identifier for each ofnetwork interface devices 28 may be different, the framing delimiter maybe the same for each of network interface devices 28.

In this manner, PON 10 utilizes the self-identifying background patterntechnique to identify the rogue network interface device from networkinterface devices 28. In some examples, OLT 12 may be able to identifythe rogue network interface device in the order of 10 milliseconds,rather than many hundreds or thousands of milliseconds, as is requiredfrom some other conventional techniques.

As described above, the optical signal from rogue network interfacedevice collides with the optical signals from the other networkinterface devices 28, causing bit errors in the reconstruction of theoptical signals from the non-rogue network interface devices. Byidentifying the rogue network interface device within 10 milliseconds,OLT 12 may be able to quarantine the rogue network interface device inthe order of 10 milliseconds. The order of magnitude improvement usingthe self-identifying background patterns technique is directly relatedto the outage time subscriber devices 30 may experience when a roguenetwork interface device failure occurs.

For example, once OLT 12 identifies the rogue network interface device,OLT 12 may disable (e.g., quarantine) the rogue network interfacedevice. OLT 12 may output an instruction to the rogue network interfaceto disable the upstream transmission so that there is no colliding withthe optical signals of the non-rogue network interface devices.Disabling upstream transmission should not be confused with turning offthe laser as part of transmitting data. For example, as normal part ofdata transmission, network interface devices 28 turn off their lasersduring timeslots for which they are not assigned. Disabling upstreamtransmission may be considered as a hard shutdown of the laser. Forexample, in response to a request to disable upstream transmission, thecontroller of the rogue network interface device may turn off the powerto the laser or turn off the power to the laser driver. In this way, thecontroller of the rogue network interface device may be able to disableupstream transmission even if the controller cannot control turning offthe laser during timeslots for which it is not assigned.

Moreover, another advantage of the self-identifying background patternstechniques may be that the predefined data pattern includes a relativelyhigh number of data transitions (e.g., one/zero transitions thatprovides 40% to 60% transitions). This allows OLT 12 to quickly detectthe rogue condition. For instance, as described above, OLT 12 determinesthat a rogue network interface device exists when optical power isreceived in the quiet timeslot. With a high number of data transitions,OLT 12 may be able determine that optical power exists in the quiettimeslot more quickly than other background patterns. For instance, ONUsor ONTs that use an all-zero background pattern may be difficult todetect as rogue network interface devices because the optical power ofan all zero pattern is low.

The preceding described an example of the self-identifying backgroundpatterns technique. The following describes an example of thedifferential pattern transition density technique. As described above,PON 10 may be configured to implement the self-identifying backgroundpatterns technique or the differential pattern transition densitytechnique. In some examples, PON 10 may be configured to implement theself-identifying background patterns technique, and if theself-identifying background patterns technique is unable to identify therogue network interface device, PON 10 may utilize the differentialpattern transition density technique.

For example, as described above, the laser driver includes an APC loopthat controls the amount of current flowing through the laser. Inaddition to relying on data transitions of the APC loop to functionproperly, in some examples, the APC loop may require the laser to turnoff periodically, such as during timeslots not assigned to the one ofnetwork interface devices 28 that includes the laser driver, to functionproperly. For properly functioning (e.g., non-rogue) network interfacedevices 28, turning off the laser during timeslots not assigned to theone of network interface device 28 that includes the laser is sufficientto keep the APC loop of the laser driver functioning properly.

However, for the rogue network interface device, the APC loop may notfunction properly because the laser does not turn off and remains on atall timeslots. Because the APC loop does not function well for the roguenetwork interface device, the optical signal outputted by the roguenetwork interface device may be error prone. In other words, in somenetworks with a rogue network interface device, the APC loop has beencompromised resulting in a very high error rate to OLT 12.

For instance, the optical signal representing the data from respectivesubscriber devices 30 may include errors causing OLT 12 to reconstructdata that is different from the data transmitted by the respectivesubscriber devices 30. In addition, if the rogue network interfacedevice is transmitting a predefined data pattern that includes itsunique identifier, a malfunctioning APC loop may result in OLT 12 beingunable to properly reconstruct the received data pattern. For example,the identifier that OLT 12 reconstructs may not be the identifier of therogue network interface device because the errors induced by themalfunctioning APC loop of the laser driver.

In the differential pattern transition density technique, OLT 12 may notrely on the precise digital bit values in the optical signal todetermine which network interface device 28 is the rogue networkinterface device. Rather, OLT 12 may determine a change in transitiondensity in the optical signal received in the quiet timeslot to identifythe rogue network interface device (e.g., presence of a high error rate,uncontrolled laser of a rogue network interface device).

For example, during timeslots to which network interface devices 28 arenot assigned, each one of network interface devices 28 may output afirst predefined data pattern with a first data transition density,where the data transition density is equal to a ratio of logical ones(digital highs) to logical zeros (digital lows). This first predefineddata pattern may be the same for all network interface devices 28. Evenif the predefined data patterns are different for network interfacedevices 28, the data transition density may be the same for the datapatterns for network interface devices 28.

In this example, OLT 12 may determine the data transition density of thereceived optical signal (e.g., ratio of received logical ones toreceived logical zeros). In this case, because of the compromised APCloop of the rogue network interface device, the data transition densityof the optical signal received by OLT 12 in the quiet timeslot may bedifferent than the data transition density of the first predefined datapattern transmitted by the controller of the rogue network interfacedevice.

As an example, the transition density duty cycle of the first predefineddata 25% or 75%, as two examples. In this example, if there is a 12% biterror rate, then the transition density measured by OLT 12 may be 38%(if originally 25%) or 63% (if originally 75%). The techniques describedin this disclosure, even with a 12% bit error rate, OLT 12 may be ableto determine which one of network interface devices 28 is the roguenetwork interface device. However, with a 12% bit error rate, OLT 12 maynot be able to properly reconstruct the unique identifier of networkinterface devices 28 (e.g., be able to accurately determine which one isthe rogue network interface device).

In the differential pattern transition density technique, OLT 12 maymeasure the transition density of the optical signal received in thequiet timeslot when controllers of network interface devices 28 areoutputting the first predefined data pattern with the first transitiondensity for timeslots to which they are not assigned. OLT 12 may storethe measured transition density when the controllers of networkinterface devices 28 were outputting the first predefined data patternduring timeslots not assigned to network interface devices 28 to whichthe controllers belong.

OLT 12 may then perform a linear search to identify the rogue networkinterface device. For example, OLT 12 may cause network interface device28A to output a second predefined data pattern with a second differenttransition density. In some examples, the transition density of firstpredefined data pattern and the second predefined data pattern may besufficiently different (e.g., if the transition density of the firstpredefined data pattern is 25%, then the transition density of thesecond predefined data patter is 75%, or vice-versa). In some examples,while OLT 12 may cause the controller of network interface device 28A tooutput the second predefined data pattern in timeslots not assigned tonetwork interface device 28A, the controllers of the remaining networkinterface devices 28 may keep outputting the first predefined datapattern during timeslots not assigned to the remaining network interfacedevices 28.

In this example, OLT 12 may measure the transition density in the quiettimeslot, and compare the measured transition density to the storedtransition density. If the measured transition density is the same asthe stored transition density, then OLT 12 may determine that networkinterface device 28A is not the rogue network interface device. This isbecause the controller of network interface device 28A is outputting thesecond predefined data pattern. If network interface device 28A were therogue network interface device, then OLT 12 would measure a differenttransition density than the stored transition density since the secondpredefined data pattern would propagate as an optical signal in thequiet timeslot.

If the measured transition density is different than the storedtransition density, then OLT 12 may determine that network interfacedevice 28A is the rogue network interface device. This is because thecontroller of network interface device 28A is outputting the secondpredefined data pattern with a different transition density than thefirst predefined data pattern, and the controllers of the remainingnetwork interface devices 28 are outputting the first predefined datapattern. If OLT 12 determines that the transition density of thereceived optical signal changed, then the cause of the change is mostlikely because network interface device 28A switched from outputting thefirst predefined data pattern to the second predefined data pattern.

In the case that network interface device 28A is not the rogue networkinterface device, OLT 12 may cause network interface device 28B toswitch from the first predefined data pattern to the second predefineddata pattern. OLT 12 may then repeat measuring the transition density,comparing the measured transition density to the stored transitiondensity, and determining whether network interface device 28B is therogue network interface device. If network interface device 28B is notthe rogue network interface device, OLT 12 may keep searching throughnetwork interface devices 28 until the rogue network interface device isidentified.

For example, OLT 12 may instruct controllers of network interfacedevices 28 to transmit a first data pattern having a first datatransition density during timeslots to which network interface devices28 are not assigned. OLT 12 may determine a data transition density ofan optical signal received during the quiet timeslot when controllers ofnetwork interface devices 28 are transmitting the first data patternduring timeslots to which they are not assigned. OLT 12 may repeatedlyinstruct controllers of respective network interface devices 28 tosequentially transmit a second data pattern having a second datatransition density during timeslots to which the respective networkinterface devices 28 are not assigned until the rogue network interfacedevice is identified. OLT 12 may repeatedly determine a data transitiondensity of an optical signal received during the quiet timeslot when oneof the controllers of one of network interface devices 28 istransmitting the second data pattern having the second data transitiondensity during timeslots to which it is not assigned until the roguenetwork interface device is identified. OLT 12 may determine that thenetwork interface device that is transmitting the second data patternhaving the second data transition density is the rogue network interfacedevice based on the data transition density of the optical signal whennetwork interface devices 28 were transmitting the first data patternduring timeslots to which they were not assigned being different thanthe data transition density of the optical signal when the rogue networkinterface device was transmitting the second data pattern duringtimeslots to which it was not assigned.

Because the differential pattern transition density technique does notrequire determining the precise digital bit values, the differentialpattern transition density technique may function even under extremesignal degradation cases due to the APC loop of the rogue networkinterface device being saturated or compromised. Also, similar to above,once OLT 12 identifies the rogue network interface device, OLT 12 maydisable (e.g., quarantine) the rogue network interface device asdescribed above.

In both the self-identifying background patterns technique and thedifferential pattern transition density technique, OLT 12 may not needto stop upstream transmission of data from subscriber devices 30 whileattempting to identify the rogue network interface device. For example,during timeslots assigned to network interface devices 28, networkinterface devices 28 keep outputting data from respective subscriberdevices 30. In this way, no halt to upstream transmission services maybe needed. Moreover, both of these techniques may reduce cost associatedwith network monitoring and manual isolation when problems arise from arogue network interface device.

Some other techniques sequentially disable the laser to identify therogue network interface device, which may take on the order of secondsto identify the rogue network interface device, and results in upstreamdata transmission interruption for seconds. For example, if there are128 network interface devices, and the 128^(th) network interface deviceis the rogue network interface device, then until OLT 12 reaches the128^(th) network interface device, the upstream transmission of the128^(th) network interface device is halted.

Furthermore, in some cases, disabling a laser may clear the roguebehavior of rogue network interface device if the rogue behavior is dueto a lockup in the laser average power loop. However, the rogue behaviormay return. Therefore, disabling the laser may in some cases result inOLT 12 not being able to identify the rogue network interface device.

In the self-identifying background patterns technique, OLT 12 may beable to identify the rogue network interface device in the order of afew milliseconds, which is much better than the seconds that it takesthe conventional techniques. In the differential pattern transitiondensity technique, it may take OLT 12 the same amount of time toidentify the rogue network interface device as the conventionaltechnique. However, OLT 12 may not need to disable upstream transmissionof network interface devices 28 until OLT 12 identifies the roguenetwork interface device.

FIG. 2 is a block diagram illustrating an example of a network interfacedevice in accordance with the techniques described in this disclosure.For purposes of illustration, FIG. 2 illustrates network interfacedevice 28A in greater detail. Network interface devices 28B-28N may besubstantially similar to network interface device 28A.

As illustrated, network interface device 28A includes controller 32,laser driver 38, and laser 40 for upstream transmission. In addition,network interface device 28A includes components for receivingdownstream transmission from OLT 12, such as a photodiode, atransimpedance amplifier (TIA), limiting amplifier, and a clock-and-datarecovery (CDR) unit. The components used for receiving optical signalsare not illustrated for ease of illustration. In general, even ifnetwork interface device 28A is a rogue network interface device, theremay be no effect on the downstream transmission from OLT 12. Also,controller 32 may be a media access control (MAC) controller. In someexamples, controller 32 may control both the upstream transmission anddownstream reception for network interface device 28A. In some examples,network interface device 28A may include separate controllers forupstream and downstream.

Controller 32 may output data from subscriber devices 30, duringtimeslots assigned to network interface device 28A, or output one of theexamples of predefined data patterns, during timeslots not assigned tonetwork interface device 28A, via data line 34 to laser driver 38. Insome examples, data line 34 may be differential data lines.

Also, controller 32 may output a control signal, via control line 36, tolaser driver 38 to instruct laser driver 38 to turn on or turn off laser40. In some examples, control line 36 may be differential control lines.During timeslots when network interface device 28A is to output anoptical signal representing the data outputted by subscriber devices30A, controller 32 may output a voltage as a control signal via controlline 36 to instruct laser driver 38 to energize (turn on) laser 40.Laser driver 38 may control the amount of current that flows to laser 40to cause laser 40 to output the optical signal via fiber link 27A thatrepresents the data from subscriber devices 30A.

During timeslots when network interface device 28A is not to output anoptical signal, controller 32 may output examples of the predefined datapatterns described above, via data line 34, and also output a voltage asa control signal via control line 36 to instruct laser driver 38 tode-energize (turn off) laser 40. Even though controller 32 is outputtingan example of the predefined data pattern via data line 34 to laserdriver 38, because laser driver 38 turns off laser 40, the predefineddata pattern may not propagate as an optical signal via fiber line 27A.

However, in some cases, controller 32 may instruct laser driver 38 toturn off laser 40, but laser 40 may not turn off (e.g., laser 40 isenergized outside of the control of controller 32), resulting in networkinterface device 28A being a rogue network interface device. Forinstance, due to a mechanical malfunction between where control line 36couples to laser driver 38, laser driver 38 may not receive theinstruction to turn off laser 40, and may keep laser 40 turned on. Asanother example, due to an electrical malfunction of laser driver 38,laser driver 38 may be stuck in a state where laser driver 38 keepslaser 40 turned on, regardless of the control signal outputted bycontroller 32.

In accordance with the self-identifying background patterns technique,controller 32 may store the unique identifier for network interfacedevice 28A. During timeslots not assigned to network interface device28A, controller 32 may output the predefined data pattern that includesthe unique identifier via data line 34 to laser driver 38 and aninstruction to turn off laser 40 via control line 36. If laser 40 is notunder control of controller 32 (e.g., laser 40 is still on), then laser40 may output an optical signal that represents the predefined datapattern with the embedded unique identifier. OLT 12 may receive thepredefined data pattern with the embedded unique identifier of networkinterface device 28A, and identify network interface device 28A as therogue network interface device based on the unique identifier (e.g.,identify a rogue network interface device 28A from the plurality ofnetwork interface devices 28 as one of the network interface deviceshaving a unique identifier that is same as the unique identifierembedded in the data pattern received during the quiet timeslot).

In accordance with the differential pattern transition densitytechnique, controller 32 may output a first predefined data patternhaving a first data transition density during timeslots not assigned tonetwork interface device 28A. Then, controller 32 may receiveinstruction from OLT 12, via a downstream reception which is unaffectedeven if network interface device 28A is rogue, to switch from the firstpredefined data pattern to a second predefined data pattern having asecond data transition density. Controller 32 may output the secondpredefined data pattern during timeslots not assigned to networkinterface device 28A. If OLT 12 determines that there was a change inthe data transition density of the optical signal received in the quiettimeslot after controller 32 switched to the second predefined datapattern, OLT 12 may identify network interface device 28A as the roguenetwork interface device.

In some examples, if network interface device 28A is identified as therogue network interface device, OLT 12 may disable network interfacedevice 28A (e.g., output instructions to quarantine the rogue networkinterface device). In general, to disable network interface device 28A,controller 32 may receive a downstream transmission to disable networkinterface device 28A. In response, controller 32 may open one or both ofswitches 42A and 42B to disable one or both of laser driver 38 and laser40. There may be other ways in which to disable the rogue networkinterface device, and the preceding technique is one example way inwhich to disable the rogue network interface device.

FIG. 3 is a block diagram illustrating an example of an optical lineterminal (OLT) in accordance with the techniques described in thisdisclosure. As illustrated, OLT 12 includes processor 44 and memory 46,and transmits and receives optical signals via fiber link 13. In someexamples, OLT 12 may include one or more processors, and processor 44 isillustrated as generically representing one or more processors.Processor 44 of OLT 12 may be configured to determine whether a roguenetwork interface device exists in PON 10. For example, processor 44 mayassign each one of network interface devices 28 with a timeslot foroutputting an optical signal for upstream transmission (e.g., assignallocation to each one of network interface devices 28), and reserve onetimeslot as a timeslot where none of network interface devices 28outputs an optical signal (e.g., the quiet timeslot, also referred to asunassigned allocation, that is not allocated to any of the plurality ofnetwork interface devices 28 for upstream transmission). Processor 44may determine whether optical power exists in the quiet timeslot anddetermine that a rogue network interface device exists if there issufficient optical power in the quiet timeslot.

In addition, processor 44 may be configured to determine which one ofnetwork interface devices 28 is the rogue network interface deviceutilizing the example techniques described in this disclosure. Forinstance, memory 46 stores values used to determine which one networkinterface devices 28 is the rogue network interface device, andprocessor 44 uses the stored values in memory 46 to identify the roguenetwork interface device.

For example, in the self-identifying background patterns technique,processor 44 may reconstruct the predefined data pattern with theembedded unique identifier from the optical signal received in the quiettimeslot. Memory 46 may store the unique identifiers for each of networkinterface devices 28, and processor 44 may compare the reconstructedunique identifier with the unique identifiers stored in memory 46 todetermine which one of network interface devices 28 is the rogue networkinterface device.

In the differential pattern transition density technique, networkinterface devices 28 may be transmitting the first predefined datapattern having the first data transition density. Processor 44 maydetermine (e.g., measure) the data transition density of the opticalsignal received in the quiet timeslot, and store the determined datatransition density in memory 46. Processor 44 may then instruct a firstone of network interface devices 28 to transmit the second predefineddata pattern having the second data transition density. Processor 44 maydetermine the data transition density of the optical signal received inthe quiet timeslot when the first one of network interface devices 28transmitted the second predefined data pattern. Processor 44 may comparethe determined data transition density with the stored data transitiondensity value, and based on the comparison determine whether the firstone of network interface devices 28 is the rogue network interfacedevice. If it is not, processor 44 may repeat the steps with the secondone of network interface devices 28, and so forth, until processor 44identifies the rogue network interface device.

In some examples, albeit not a requirement, processor 44 may firstattempt the self-identifying background patterns technique to identifythe rogue network interface device. If unsuccessful, processor 44 mayattempt the differential pattern transition density technique. In thiscase, processor 44 may instruct the controllers of each one of networkinterface devices 28 to switch from the predefined data pattern thatincludes the unique identifier to the predefined data pattern having thefirst data transition density, and then cause the controller of each oneof network interface devices 28 to sequentially or selectively (e.g., ina linear search) transmit the predefined data pattern having the seconddata transition density. In some examples, if processor 44 is stillunable to identify the rogue network interface device, processor 44 mayapply conventional techniques (e.g., disable network interface devices28 and enable network interface devices 28, sequentially or selectively,until the rogue network interface device is identified).

FIG. 4 is a flowchart illustrating an example method of operation of anOLT in accordance with techniques described in this disclosure. In theexample illustrated in FIG. 4, processor 44 of OLT 12 may reconstruct adata pattern from an optical signal received from one of a plurality ofnetwork interface devices 28 in a quiet timeslot (e.g., unassignedallocation), where none of network interface devices 28 are to transmitoptical signals in the quiet timeslot (50). Processor 44 may determinewhich one of network interface devices 28 transmitted the optical signalduring the quiet timeslot based on the reconstructed data pattern toidentify a rogue network interface device (52).

For instance, to reconstruct the data pattern, processor 44 may beconfigured to reconstruct a unique identifier embedded in the datapattern. To determine which one of network interface devices 28transmitted the optical signal in the quiet timeslot, processor 44 maybe configured to compare the reconstructed unique identifier to uniqueidentifiers for each of the network interface devices stored in memory46, and determine which one of network interface devices 28 transmittedthe optical signal during the quiet timeslot based on the comparison.

As another example, processor 44 may be configured to reconstruct afirst data pattern from a first optical signal received in the quiettimeslot, and determine a first transition density of the reconstructedfirst data pattern. In this example, processor 44 may not need toresolve the specific bit values, and it may be sufficient that processor44 is able to approximate the data transition density even if some ofthe bit values are incorrect.

Processor 44 may also be configured to instruct a controller of a firstnetwork interface device to transmit a second data pattern having asecond transition density during one or more timeslots to which thefirst network interface device is not assigned (e.g., in a timeslot notreserved for the first network interface device). In this case,reconstructing the data pattern includes reconstructing the data patternwhen the controller of the first network interface device istransmitting the second data pattern during timeslots to which the firstnetwork interface device is not assigned.

Processor 44 may determine a second transition density of thereconstructed data pattern when the controller of the first networkinterface device is transmitting the second data pattern duringtimeslots to which the first network interface device is not assigned,and compare the second transition density to the first transitiondensity. In this example, to determine which one of the networkinterface devices transmitted the optical signal during the quiettimeslot, processor 44 may be configured to determine whether the firstnetwork interface device transmitted the optical signal in the quiettimeslot based on the comparison.

FIG. 5 is a flowchart illustrating another example method of operationof an OLT in accordance with techniques described in this disclosure. Inthis example, processor 44 may reconstruct a data pattern, which mayinclude a unique identifier, from an optical signal received from one ofa plurality of network interface devices 28 in a quiet timeslot (e.g.,unassigned allocation), where none of network interface devices 28 areto transmit optical signals in the quiet timeslot (54). Processor 44 maycompare the unique identifier to the unique identifiers stored in memory46 for respective network interface devices (56). Processor 44 maydetermine which one of the network interface devices transmitted theoptical signal during the quiet timeslot based on the comparison (i.e.,based on a unique identifier match) to identify a rogue networkinterface device (58).

FIG. 6 is a flowchart illustrating another example method of operationof an OLT in accordance with techniques described in this disclosure. Inthis example, processor 44 may determine a data transition density of afirst optical signal received from one of a plurality of networkinterface devices 28 in a quiet timeslot (e.g., unassigned allocation),where none of the network interface devices are to transmit opticalsignals in the quiet timeslot, and where the first optical signalrepresents a first data pattern having a first data transition density(60). Processor 44 may instruct a controller of a current (e.g., first)network interface device to transmit a second data pattern having asecond data transition density during timeslots to which the current(e.g., first) network interface device is not assigned (62).

Processor 44 may be configured to determine a data transition density ofa second optical signal received in the quiet timeslot when thecontroller of the current (e.g., first) network interface device istransmitting the second data pattern having the second data transitiondensity during timeslots to which the first network interface device isnot assigned (64). Processor 44 may be configured to compare thedetermined data transition density of the first optical signal with thedetermined data transition density of the second optical signal (66).

Processor 44 may then determine whether there is a difference in thedetermined data transition density of the first optical signal with thedetermined data transition density of the second optical signal based onthe comparison (68). If processor 44 determines that there is adifference (YES of 68), processor 44 may determine that the currentnetwork interface device is a rogue network interface device and disablethe current network interface device (72). If processor 44 determines isno difference (NO of 68), processor 44 may determine that the currentnetwork interface device is not the rogue network interface device andset the next network interface device (e.g., second network interfacedevice) as the current network interface device (70). Processor 44 maythen repeat the above steps until processor 44 identifies and disablesthe rogue network interface device.

FIG. 7 is a flowchart illustrating an example method of operation ofnetwork interface device in accordance with techniques described in thisdisclosure. In this example, controller 32 of network interface device28A may be configured to cause laser driver 38 to transmit data receivedfrom one or more subscriber devices 30A in timeslots assigned to networkinterface device 28A (74). Controller 32 of network interface device 28Amay be configured to cause laser driver 38 to transmit a predefined datapattern used for rogue network interface device identification duringtimeslots to which network interface device 28A is not assigned (76).

For example, to cause laser driver 38 to transmit the predefined datapattern, controller 32 may be configured to transmit a unique identifierof network interface device 28A. As another example, controller 32 maybe configured to transmit a first predefined data pattern having a firstdata transition density during timeslots to which network interfacedevice 28A is not assigned, and receive an instruction to switch fromthe first predefined data pattern to a second predefined data patternhaving a second, different data transition density. In this example, tocause laser driver 38 to transmit the predefined data pattern,controller 32 may be configured to cause laser driver 38 to transmit thesecond predefined pattern during timeslots to which network interfacedevice 38 is not assigned, in response to receiving the instruction toswitch from the first predefined data pattern to the second predefineddata pattern.

In examples where controller 32 causes laser driver 38 to transmit aunique identifier, subsequent to transmitting the unique identifier,controller 32 may receive instructions to transmit a first data patternhaving a first data transition density during timeslots to which networkinterface device 28A is not assigned. Controller 32 may transmit thefirst data pattern having the first data transition density duringtimeslots to which network interface device 28A is not assigned.Subsequent to transmitting the first data pattern having the first datatransition density, controller 32 may receive instructions to transmit asecond data pattern having a second data transition density duringtimeslots to which network interface device 28A is not assigned.Controller 32 may transmit the second data pattern having the secondtransition density during timeslots to which network interface device28A is not assigned.

FIG. 8 is a flowchart illustrating another example method of operationof an OLT in accordance with techniques described in this disclosure. Asillustrated, OLT 12 may receive a data pattern, embedded with a uniqueidentifier, from an optical signal received during a quiet timeslot,where the quiet timeslot is a timeslot that is not allocated to any of aplurality of network interface devices 28 for upstream transmission(e.g., none of network interface devices 28 is to transmit upstream dataduring the quiet timeslot) (78). In some examples, OLT 12 may firstdetect that one of the plurality of network interface devices 28 istransmitting during the quiet timeslot, and in response to detectingthat one of the plurality of network interface devices 28 istransmitting during the quiet timeslot, OLT 12 may instruct respectivecontrollers 32 of one or more of the plurality of network interfacedevices 28 to transmit respective unique identifiers during timeslots towhich the respective plurality of network interface devices 28 are notassigned. OLT 12 may then receive the data pattern, embedded with theunique identifier, from the optical signal received during the quiettimeslot.

OLT 12 may identify a rogue network interface from the plurality ofnetwork interface devices 28 as one of the network interface deviceshaving a unique identifier that is same as the unique identifierembedded in the data pattern received during the quiet timeslot (80).For example, OLT 12 may store the unique identifiers for each of theplurality of network interface devices 28. OLT 12 may compare theembedded unique identifier in the received data pattern with respectiveunique identifiers of one or more of network interface devices 28. Inthis example, OLT 12 may identify the rogue network interface devicebased on the comparison. In some examples, in identifying the roguenetwork interface device, OLT 12 may not need to disable the upstreamtransmission of network interface devices 28 during their respectiveassigned timeslots.

OLT 12 may determine whether identifying the rogue network interfacedevice was successful (82). For instance, due to the design of the APCloop respective laser drivers 38 of respective network interface devices28, it may be possible that OLT 12 cannot reconstruct the uniqueidentifier for the rogue network interface device, and therefore, maynot be able to identify the rogue network interface device.

If OLT 12 determines that identifying the rogue network interface deviceis successful (YES of 82), OLT 12 may output instructions to quarantinethe rogue network interface device (84). For example, OLT 12 may outputinstructions that instruct controller 32 of the rogue network interfacedevice to disable power to one or both of laser driver 38 of the roguenetwork interface device or laser 40 of the rogue network interfacedevice. There may be other ways in which OLT 12 quarantines the roguenetwork interface device. Also, in some cases, when the rogue networkinterface device is quarantined, the rogue network interface device maystill receive downstream data.

If OLT 12 determines that identifying the rogue network interface deviceis not successful (NO of 82), OLT 12 may instruct controllers 32 ofnetwork interface devices 28 to transmit a first data pattern having afirst data transition density during timeslots to which networkinterface devices 28 are not assigned (86). OLT 12 may then determine adata transition density of a second optical signal received during thequiet timeslot (88).

Next, OLT 12 may repeatedly instruct controllers 32 of respectivenetwork interface devices 28 to sequentially transmit a second datapattern having a second data transition density during timeslots towhich the respective network interface devices 28 are not assigned untilthe rogue network interface device is identified (90). OLT 12 may alsorepeatedly determine a data transition density of a third optical signalreceived during the quiet timeslot until the rogue network interfacedevice is identified (92). Based on the data transition density of thethird optical signal being different than the data transition density ofthe second optical signal, OLT 12 may determine that the networkinterface device that is transmitting the second data pattern having thesecond data transition density is the rogue network interface device(94). Once the rogue network interface device is identified, OLT 12 mayoutput instructions to quarantine the rogue network interface device(96).

FIG. 9 is a block diagram illustrating another network, in accordancewith one or more aspects of this disclosure. For example, FIG. 9illustrates a multiple wavelength system 98. One example of system 98 isan ITU-T G.989 (NGPON-2) conforming system. System 98 includes OLTs100A-100N, which may each be similar to OLT 12 of FIG. 1. For ease ofillustration, the various components that couple to OLTs 100 for voice,data, and video, illustrated in FIG. 1, are not illustrated in FIG. 9.

In system 98, each one of OLTs 100A-100N may transmit downstream opticalsignals and receive upstream optical signals at specific wavelengthsthat are different from one another. For example, OLT 100A transmitsoptical signals at a first downstream wavelength, and receives opticalsignals at a first upstream wavelength. OLT 100N transmits opticalsignals at a second downstream wavelength, and receives optical signalsat a second upstream wavelength. Each of these downstream wavelengths isdifferent than each of the other downstream wavelengths and each of theupstream wavelengths. Each of these upstream wavelengths is differentthan each of the other upstream wavelengths and each of the downstreamwavelengths.

In some examples, OLTs 100A-100N may not all be the product of the samecompany. In some examples, OLTs 100A-100N may be located in differentgeographical locations. In some examples, OLTs 100A-100N may be locatedtogether within the same chassis or located together within proximity ofone another. In some examples, rather than having multiple OLTs100A-100N, system 98 may include one OLT with multiple transmitters andreceivers where each transmitter is configured to transmit downstreamoptical signals at different downstream wavelengths, and each receiveris configured to receive upstream optical signals at different upstreamwavelengths (where the downstream and upstream wavelengths are alsodifferent). For ease of description, the techniques are described withexamples that include multiple OLTs (e.g., OLTs 100A-100N).

Each one of OLTs 100A-100N is associated with (e.g., assigned to) a setof network interface devices. For example, OLT 100A is associated withset of network interface devices 104A, and OLT 100N is associated withset of network interface devices 104B. Set of network interface devices104A includes network interface devices 106A-106N, and set of networkinterface devices 104B includes network interface devices 108A-108N.

Network interface devices 106A-106N and 108A-108N may be similar tonetwork interface devices 28. For ease of illustration and description,the subscriber devices that connect to respective network interfacedevices 106A-106N and 108A-108N are not illustrated in FIG. 9.

In some examples, the upstream and downstream capabilities of networkinterface devices 104A-104N and 106A-106N may be tunable. For instance,as described above, OLT 100A may be configured to transmit downstreamoptical signals with a first downstream wavelength and configured toreceive upstream optical signals with a first upstream wavelength. Inthe example of FIG. 9, network interface devices 106 may be tuned totransmit optical signals at the first upstream wavelength and receiveoptical signals at the first downstream wavelength. Similarly, networkinterface devices 108 may be tuned to transmit optical signals at thesecond upstream wavelength at which OLT 100N is configured to receiveoptical signals, and tuned to receive optical signals at the seconddownstream wavelength at which OLT 100N is configured to transmitoptical signals.

In some examples, network interface devices 106 and 108 may be tunablefor distinct wavelengths. For instance, network interface devices 106and 108 may be tunable to transmit upstream optical signals withwavelength X or with wavelength Y, and not wavelengths intermediate to Xand Y, or wavelengths other than X or Y. In this example, OLT 100A maybe configured to receive upstream optical signals with wavelength X, andOLT 100B may be configured to receive upstream optical signals withwavelength Y. The same may be true for the tuning for the reception ofdownstream optical signals.

As illustrated, system 98 includes wave division multiplexer (WDM) 102.In the downstream, WDM 102 receives downstream optical signals atrespective wavelengths from OLTs 100A-100N, and filters the downstreamoptical signals so that network interface devices 106 only receive thedownstream optical signals with the first downstream wavelength, and sothat network interface devices 108 only receive the downstream opticalsignals with the second downstream wavelength. In the upstream, WDM 102receives upstream optical signals at respective wavelengths from networkinterface devices 106 and network interface devices 108, and filters theupstream optical signals so that OLT 100A only receives the opticalsignals with first upstream wavelength, and so that OLT 100N onlyreceives the optical signals with the second upstream wavelength.

Although a single WDM 102 is illustrated in FIG. 9, in some examplesthere may be multiple WDMs located throughout system 98. As one example,a first WDM may couple to OLTs 100A-100N, and couple to a second WDM viaa first fiber link and a third WDM via a second fiber link. The secondWDM may be proximate to network interface devices 106, and the third WDMmay be proximate to network interface devices 108. Other suchconfigurations are possible to allow OLTs 100A-100N to communicate withnetwork interface devices 106A-106N and 108A-108N.

In some examples, if network interface device 106A becomes rogue (e.g.,transmits upstream optical signals during one or more timeslots to whichit is not assigned), OLT 100A may be able to determine that networkinterface device 106A is rogue using the above example techniques ifnetwork interface device 106A is still transmitting upstream opticalsignals at the first upstream wavelength. However, in some cases, it maybe possible for network interface device 106A to become rogue and totransmit upstream optical signals not at the first upstream wavelength,but at a different upstream wavelength (e.g., the second upstreamwavelength). In this example, OLT 100A may not be able to determine thatnetwork interface device 106A is rogue because OLT 100A would notreceive an optical signal in the quiet timeslot of OLT 100A (again,network interface device 106A is rogue and not transmitting opticalsignals at the wavelength that OLT 100A is configured to receive, whichis why OLT 100A does not receive the optical signal in the quiettimeslot although network interface device 106A is rogue). For instance,because network interface device 106A is transmitting an optical signalwith a wavelength that OLT 100A is does not receive, WDM 102 may notroute the optical signal from network interface device 106A to OLT 100A.

For instance, assume that rather than transmitting optical signals withthe first upstream wavelength, network interface device 106A transmitsoptical signals with second upstream wavelength. In this example, WDM102 may route the optical signals from network interface 106A to OLT100N. In this case, OLT 100N may detect an optical signal in the quiettimeslot of OLT 100N. However, because network interface device 106Abelongs to set of network interfaces 104A, OLT 100N may not be able tocontrol network interface device 104A, making it difficult for OLT 100Nto determine which network interface device is rogue.

For example, OLTs 100A-100N and network interface devices 106 and 108may be configured to implement the “self-identifying background patternstechnique” and/or the “differential pattern transition technique”described above. However, if network interface device 106A is rogue andtransmitting an optical signal at the wavelength that OLT 100A does notreceive (e.g., is filtered out by WDM 102), it may be difficult toimplement the self-identifying background patterns technique and/or thedifferential pattern transition technique, and difficult to quarantinethe rogue network interface device. Although network interface device106A is described as being the rogue network interface device, it shouldbe understood that the techniques are equally applicable to any one ofnetwork interface devices 106 or 108 being rogue.

In the example illustrated in FIG. 9, in accordance with theself-identifying background pattern, network interface device 106A maytransmit its unique identifier during one or more timeslots to which itis not assigned and perform such transmission with an optical signalwith the second upstream wavelength, rather than the first upstreamwavelength. WDM 102 may forward the transmission from network interfacedevice 106A to OLT 100N. OLT 100N may reconstruct the unique identifierfor network interface device 106A.

In some examples, OLT 100N may store a lookup table with the uniqueidentifiers for all network interface devices 106 and 108 associatedwith each of OLTs 100 in system 98, even though network interfacedevices 106 are not associated with OLT 100N. From the lookup table, OLT100N may determine that network interface device 106A is rogue. However,because OLT 100N cannot transmit downstream information to networkinterface device 106A, OLT 100N may not be able to disable (e.g.,quarantine) network interface device 106A.

For instance, OLT 100N is configured to transmit downstream opticalsignals at the second downstream wavelength. In this case, WDM 102 mayforward downstream optical signals with the second downstream wavelengthto set of network interface devices 104B (e.g., network interfacedevices 108). Therefore, network interface device 106A may not receivethe disable instruction from OLT 100N to remove power from its laserdriver or laser.

In this sense, OLT 100N may be considered as a detector OLT because OLT100N is configured to detect and determine which network interfacedevice is rogue. However, OLT 100N cannot control the rogue networkinterface device, and a controller OLT may be needed to control therogue network interface device.

As one example, in addition to storing the unique identifiers for eachone of network interface devices 106 and 108, OLT 100N may also storeinformation indicating with which OLT each one of network interfacedevices 104 is associated. OLT 100N may store such information in thesame list as the list of unique identifiers or in a separate list.

OLT 100N may determine that OLT 100A is associated with networkinterface device 106A. OLT 100A may be considered as the controller OLTbecause OLT 100A can control network interface device 106A.

OLT 100N may transmit a request OLT 100A to disable (e.g., quarantine)network interface device 106A. In response, OLT 100A may disable networkinterface device 106A. OLT 100N may transmit the request to OLT 100Ausing any of a variety of transmission protocols, including out of bandcommunication, as illustrated by dashed line 110.

In some examples, OLT 100N may not store a look up table of the uniqueidentifiers for all network interface devices 106 and 108 or informationthat identifies which OLTs are associated with which network interfacedevices. In these examples, in accordance with the self-identifyingbackground patterns technique, OLT 100N may reconstruct the uniqueidentifier of network interface device 106A and determine that OLT 100Nis not associated with network interface device 106A. Then, OLT 100N maybroadcast the unique identifier for network interface device 106A to oneor more other OLTs and send a request (e.g., via out of bandcommunication 110) to all other OLTs requesting the OLT that controlsnetwork interface device 106A to disable (e.g., quarantine) networkinterface device 106A. In this example, because OLT 100A is thecontroller OLT of network interface device 106A, in response to requestfrom OLT 100N, OLT 100A may disable network interface device 106A.

In this manner, by utilizing a detector OLT and a controller OLT (e.g.,the detector OLT communicates with the controller OLT), theself-identifying background patterns technique may be extended to amultiple wavelength system such as system 98. In the techniquesdescribed in this disclosure, by utilizing a detector OLT and acontroller OLT, the different pattern transition technique may also beextend to a multiple wavelength system such as system 98.

For instance, the following keeps with the example where networkinterface device 106A is the rouge network interface device (e.g.,transmitting at one or more timeslots to which it is not assignedoutside of the control of its controller OLT) that is transmittingoptical signals at the second upstream wavelength. As above, OLT 100Nmay receive an optical signal in the quiet timeslot of OLT 100N.

However, in this example, there is no unique identifier, and therefore,OLT 100N may not be able to determine whether the rogue networkinterface device exists in set of network interface devices 104A or setof network interface devices 104B. In some examples, OLT 100N mayimplement the differential pattern transition technique on networkinterface devices 108 of set of network interface devices 104B, asdescribed above. In this case, there may be no difficultly for OLT 100Nto implement the differential pattern transition technique on networkinterface devices 108 because network interface devices 108 areassociated with OLT 100N.

However, by implementing the differential pattern transition techniqueon network interface devices 108, OLT 100N may not identify the roguenetwork interface device (e.g., network interface device 106A) becausethe rogue network interface is not one of network interface devices 108.Also, because OLT 100N may not be configured to control networkinterface devices 106, OLT 100N may not be capable of causing thecontrollers of network interface devices 106 to switch data patternsfrom the first predefined data pattern with a first data transitiondensity to the second predefined data pattern with a second datatransition density.

For the differential pattern transition technique, the controllers ofnetwork interface devices 106 and 108 may be configured to transmit thefirst predefined pattern with the first data transition density duringone or more timeslots to which they are not assigned. If the controllersof network interface devices 106 and 108 are not already transmittingthe first predefined data pattern with the first data transition densityduring one or more timeslots to which they are not assigned, thedetector OLT (e.g., OLT 100N) may request all OLTs 100 to instruct thecontrollers of the network interface devices with which they areassociated to transmit the first predefined pattern with the first datatransition density during one or more timeslots to which they are notassigned. In either example, the detector OLT (e.g., OLT 100N) maydetermine the data transition density of the optical signal receivedduring the quiet timeslot.

OLT 100N may then request a first OLT to instruct a controller of afirst network interface device that is associated with the first OLT toswitch from the first predefined data pattern with the first transitiondensity to the second predefined data pattern with the second transitiondensity. In this example, the first OLT is the controller OLT becausethe first OLT controls the first network interface device associatedwith the first OLT.

OLT 100N may then determine whether the transition density of theoptical signal received in the quiet timeslot changed. If the transitiondensity changed, OLT 100N may request the first OLT to disable the firstnetwork interface device because OLT 100N determined that the firstnetwork interface device of the first OLT is rogue.

If the transition density did not change, OLT 100N may request the firstOLT to instruct the controller of the second network interface device toswitch from the first predefined pattern with the first data transitiondensity to the second predefined pattern with the second data transitiondensity. OLT 100N may determine whether the transition density changed,and if the transition density did not change, and may repeat the abovesteps until all network interface devices associated with the first OLThave been checked. If OLT 100N is still not able identify the roguenetwork interface device, OLT 100N may proceed with the next OLT andrepeat the steps until OLT 100N identifies the rogue network interfacedevice, which is then disabled.

In the above example of the differential pattern transition technique,the detector OLT (e.g., OLT 100N) dictates to the controller OLT when toswitch from the first predefined pattern with the first data transitiondensity to the second predefined pattern with the second data transitiondensity. However, the techniques described in this disclosure are not solimited. In some examples, the detector OLT may broadcast that a roguenetwork interface device exists. Then, based on some predefined criteriaor negotiation between OLTs 100, one of the other OLTs (e.g., other thanOLT 100N) may be the first to implement the differential patterntransition technique.

For instance, assume that an OLT (i.e., OLT 100B) (not shown in FIG. 9),is determined to implement the differential pattern transition techniquefirst, followed by OLT 100A. In this example, OLT 100B may instruct afirst network interface device associated with OLT 100B to switch fromthe first predefined pattern with the first data transition density tothe second predefined pattern with the second data transition density.OLT 100B may then query OLT 100N about whether the transition density inthe quiet timeslot of OLT 100N changed. If OLT 100N responds that thereis no change in the transition density, then OLT 100B may instruct asecond network interface device associated with OLT 100B to switch fromthe first predefined pattern with the first data transition density tothe second predefined data pattern with the second data transitiondensity, and query OLT 100N about any change in the transition density.

OLT 100B may keep repeating these steps until either the rogue networkinterface device is identified or until all network interface devicesassociated with OLT 100B have been checked. In this example, becausenetwork interface device 106A is rogue, the differential patterntransition technique, being implemented by OLT 100B, may not identifythe rogue network interface device.

However, OLT 100A may then implement the differential pattern transitiontechnique. In this example OLT 100A may instruct network interfacedevice 106A to switch from the first predefined data pattern with thefirst data transition density to the second predefined data pattern withthe second data transition density. OLT 100A may then query OLT 100N,and OLT 100N may indicate that the transition density of the opticalsignal received in the quiet timeslot indeed changed. OLT 100A maydetermine that network interface device 106A is the rogue networkinterface device and disable network interface device 106A.

In this manner, it may be possible to identify the rogue networkinterface device in the multiple wavelength system. For example, thedetector OLT (e.g., OLT 100N) may receive a data pattern in an opticalsignal received from one of a plurality of network interface deviceswith which the detector OLT is not configured to communicate (e.g.,network interface device 106A) in a quiet timeslot. The detector OLT maycommunicate with one or more other OLTs (e.g., one or more controllerOLTs such as OLT 100A) for determining which one of the networkinterface devices transmitted the optical signal during the quiettimeslot based on the data pattern to identify a rogue network interfacedevice. As one example, OLT 100N may transmit the identifier to OLT 100Afor network interface device 106A.

As another example, OLT 100N may instruct all other OLTs to causerespective controllers to transmit a signal with a first data transitiondensity during one or more timeslots to which they are not assigned. OLT100N may then communicate with OLT 100A (e.g., instruct OLT 100A) tocause a controller of network interface device 106A to switch to apredefined pattern with a second data transition density. If OLT 100Ndetermines that there is a change in the data transition density of theoptical signal received during the quite timeslot, OLT 100N maydetermine that network interface device 106A is rogue and communicatewith OLT 100A (e.g., instruct OLT 100A) to disable network interfacedevice 106A.

Accordingly, in the example illustrated in FIG. 9, OLT 100N may includea memory, similar to memory 46 illustrated in FIG. 3, and one or moreprocessors, similar to processor 44 illustrated in FIG. 3. The memory ofOLT 100N stores information, and the one or more processors of OLT 100Nare configured to receive a data pattern in an optical signal receivedduring a quiet timeslot, where the quiet timeslot is a timeslot that isnot allocated to any of a plurality of network interface devices (e.g.,network interface devices 106), with which OLT 100N is associated, forupstream transmission.

The one or more processors may determine that a rogue network interfacedevice from which the optical signal is received during the quiettimeslot is not a network interface device to which OLT 100N isconfigured to transmit downstream data based on the received datapattern and the stored information. For example, OLT 100N may storeinformation that includes one or more lists of unique identifiers forall network interface devices associated with each one of OLTs 100, andbased on the one or more lists determine that OLT 100N is not associatedwith the rogue network interface device, and determine which OLT isassociated with the rogue network interface device. As another example,OLT 100N may store information that includes a list of uniqueidentifiers only for the network interface devices associated with OLT100N (e.g., network interface devices 108), and based on the list, OLT100N determines that OLT 100N is not associated with the rogue networkinterface device.

OLT 100N may communicate with one or more of the other OLTs 100information to quarantine the rogue network interface device. Forinstance, in the example where OLT 100N stores the identifiers for aplurality of network interface devices, and information identifying theOLTs to which a plurality of network interface devices are associated(e.g., all network interface devices, but does not have to be allnetwork interface devices), OLT 100N may determine which OLT isassociated with rogue network interface device, and instruct that OLT toquarantine the rogue network interface device. In the example where OLT100N stores the identifiers for only the network interface device towhich it is associated, OLT 100N may broadcast the identifier for therogue interface device, and the OLT that is associated with the rogueinterface device may quarantine the rogue interface device.

FIG. 10 is a flowchart illustrating an example method of operation of anOLT in the network illustrated in FIG. 9. In the example illustrated inFIG. 10, and as described above with respect to FIG. 9, system 98includes a first OLT (e.g., OLT 100N), a set of network interfacedevices 104B associated with the first OLT, and a second OLT (e.g., OLT100A). The first OLT may receive a data pattern in an optical signalreceived during a quiet timeslot, where the quiet timeslot is a timeslotthat is not allocated to any of set of interface devices 104B (e.g., anyof network interface devices 108), that are associated with the firstOLT, for upstream transmission (112).

The first OLT may determine that a rogue network interface device fromwhich the optical signal is received during the quiet timeslot is not anetwork interface device of the set of network interface devices 104Bbased on the received data pattern (114). For example, the first OLT maydetermine based on one or more stored lists that include the identifiersfor one or more network interface devices 106 and 108 and the OLTs towhich one or more network interface devices 106 and 108 are associatedthat the rogue network interface device is not associated with the firstOLT. For instance, the first OLT may store a list of unique identifiersfor network interface devices 106 and 108 and a list of OLTs to whichnetwork interface devices 106 and 108 are associated.

As another example, the first OLT may determine based on a stored listthat include the identifiers only for one or more network interfacedevices 108 that the rogue network interface device is not associatedwith the first OLT. For instance, the first OLT may store a list ofunique identifiers only for network interface devices 108.

The first OLT may communicate with one or more other OLTs (e.g., thesecond OLT) information to quarantine the rogue network interface device(116). For instance, the first OLT may determine that the second OLT isassociated with the rogue network interface device based on the storedone or more lists and instruct the second OLT to quarantine the roguenetwork interface device. As another example, the first OLT maybroadcast the identifier for the rogue network interface device, and theOLT that is associated with the rogue network interface device mayquarantine the rogue network interface device.

FIG. 11 is a block diagram illustrating another network, in accordancewith one or more aspects of this disclosure. Like FIG. 9, FIG. 11 alsoillustrates an example of multiple wavelength system, referred to asmultiple wavelength system 118. The techniques described in the systemillustrated in FIG. 11 may be function in conjunction with the examplesystems illustrated in FIGS. 1 and 9, or may function independently ofthe example systems illustrated in FIGS. 1 and 9. For instance, FIG. 11illustrates an example in which each network interface device determineswhether it is transmitting an optical signal at a wavelength at which itis not to transmit and self-quarantines.

As illustrated in FIG. 11, system 118 includes OLTs 120A-120N, WDM 122,a first set of network interface devices 124A that includes networkinterface devices 126A-126N, and a second set of network interfacedevices 124B that includes network interface devices 128A-128N. For easeof description, the subscriber devices, as illustrated in FIG. 1,coupled to each of network interface devices 126 and 128 are notillustrated in FIG. 11. Also for ease of description, the variouscomponents that couple to OLTs 120 for voice, data, and video,illustrated in FIG. 1, are not illustrated in FIG. 11.

Similar to FIG. 9, each one of OLTs 120 may transmit downstream opticalsignal and receive upstream optical signals from different sets ofnetwork interface devices 124. For example, OLT 120A may transmit andreceive optical signals from network interface devices 126 of set 124A,and OLT 120N may transmit and receive optical signals from networkinterface devices 128 of set 124B. Accordingly, each of OLTs 120 maytransmit and receive optical signals at different wavelengths, andnetwork interface devices 126 of set 124A may transmit and receiveoptical signals at different wavelengths than network interface devices128 of set 124B. WDM 122 may transmit optical signals to the right pairof OLTs 120 and sets 124. Also, although not illustrated in FIG. 11, insome cases, OLTs 120 may communicate with one another using out of bandcommunication, such as via out of band communication 110 illustrated inFIG. 9.

In examples described above with respect to FIGS. 1-10, one way in whicha network interface device becomes rogue is by transmitting an opticalsignal during timeslots to which it is not assigned. The above exampletechniques describe ways in which an OLT (e.g., OLT 12 or one of OLTs100) determines which network interface device (e.g., which one ofnetwork interface devices 28 or which one of network interface devices106 or 108) is rogue. In some instances it may be possible for thenetwork interface device itself to determine whether it is rogue.

For example, as illustrated in FIG. 11, network interface device 126Aincludes laser 130, laser driver 132, monitor unit 134, and controller136. Network interface devices 126B-126N and 128 may include similarcomponents. Laser 130, laser driver 132, and controller 136 may besubstantially similar to laser 40, laser driver 38, and controller 32 ofnetwork interface device 28A illustrated in FIG. 2. Furthermore,although the components of network interface device 126A fortransmitting an optical signal are illustrated in FIG. 11, networkinterface device 126A also includes components for receiving opticalsignals, such as a photodiode, a transimpedance amplifier (TIA),limiting amplifier, and a clock-and-data recovery (CDR) unit. Thecomponents used for receiving optical signals are not illustrated forease.

Monitor unit 134, sometimes referred to as a “watchdog,” may beintegrated with controller 136 or external to controller 136. Monitorunit 134 may be implemented as hardware or software or firmwareexecuting on hardware. Monitor unit 134 may monitor the optical outputpower level of laser 130 (e.g., the average optical power level), andoutput a value indicative of the optical output power level tocontroller 136. Monitor unit 134 may continuously monitor the opticaloutput power level of laser 130, or periodically monitor the opticaloutput power level of laser 130. In some examples, controller 136 mayinstruct monitor unit 134 to monitor the optical output power level oflaser 130 during timeslots assigned to network interface device 126A forupstream transmission, and to monitor the optical output power level oflaser 130 during timeslots not assigned to network interface device 126Afor upstream transmission.

If monitor unit 134 outputs an optical output power level value that isgreater than a threshold during timeslots that are assigned to networkinterface device 126A, and outputs an optical output power level valuethat is less than a threshold during timeslots that are not assigned tonetwork interface device 126A, controller 136 may determine that networkinterface device 126A is operating properly. However, if monitor unit134 outputs an optical output power level value that is greater than athreshold during timeslots that are assigned to network interface device126A, but outputs an optical output power level value that is alsogreater than a threshold during timeslots that are not assigned tonetwork interface device 126A, controller 136 may determine that networkinterface device 126A is rogue. In this case, controller 136 mayquarantine network interface device 126A (e.g., disable upstreamtransmission of optical signals).

The techniques where controller 136 quarantines network interface device126A based on the monitoring of the optical power level outputted bylaser 130 may be referred to as a self-quarantining technique. Also,although this self-quarantining technique is described with respect tothe multiple wavelength system, such techniques may be applied tonon-multiple wavelength systems, such as the system illustrated inFIG. 1. For instance, this example of the self-quarantining techniquedoes not require an instruction from an OLT for quarantining purposes.However, self-quarantining may utilize additional components such asmonitor unit 134 and require monitoring of the laser output, which maynot be needed in the examples illustrated in FIGS. 1 and 9.

Furthermore, in accordance with aspects described in this disclosure,the self-quarantining technique may be utilized for situations where anetwork interface device becomes a “wavelength rogue.” As describedabove, in some examples, a network interface device becomes rogue bytransmitting optical signals during timeslots to which it is notassigned. However, in multiple wavelength systems, a network interfacedevice may be transmitting optical signals at assigned timeslots, andnot transmitting optical signals at timeslots to which it is notassigned, but may be transmitting optical signals at the incorrectwavelength.

For instance, in the example described with respect to FIG. 9, networkinterface device 106A transmits optical signals during timeslots towhich it is not assigned, and also transmits optical signals at awavelength to which it is not assigned. In some cases, it may bepossible for network interface device 126A to not transmit opticalsignals during timeslots to which it is not assigned, but may transmitoptical signals, at correct timeslots, at a wavelength to which it isnot assigned. If network interface device 126A does not transmit opticalsignals during timeslots to which it is not assigned, but transmitsoptical signals, at correct timeslots, at a wavelength to which it isnot assigned, network interface device 126A may be considered as beingwavelength rogue network interface device.

As an illustrative example, assume that network interface device 126A isassigned to OLT 120A. In this example, under normal operation, OLT 120Atransmits downstream optical signals that network interface device 126Areceives, and network interface device 126A transmit optical signals ata first wavelength that OLT 120A is configured to receive. However, itmay be possible for laser 130 of network interface device 126A to drift,causing network interface device 126A to transmit optical signals at asecond wavelength. Assume that OLT 120N is configured to receive opticalsignals at the second wavelength from network interface devices 128. Inthis example, OLT 120N may receive optical signals from networkinterface device 126A, which is a network interface device not assignedto OLT 120N.

In this example, because network interface device 126A is nottransmitting optical signals during timeslots to which it is notassigned, it may be possible that OLT 120N does not receive any opticalsignal during its quiet timeslot. For instance, if the timeslot thatnetwork interface device 126A is assigned overlaps with one or moretimeslots that one or more of network interface devices 128 is assigned,then OLT 120N may not receive optical signals during the quiet timeslotof OLT 120N because network interface device 126A is only transmittingoptical signals during timeslots to which it is assigned.

In this case, although OLT 120N may not be able to correctly determinethe digital bits transmitted by one or more network interface devices128 due to the interference from the optical signal transmitted bynetwork interface device 126A, OLT 120N may not be able to determinethat a wavelength rogue network interface device exists in system 118because there is no optical signal in the quite timeslot of OLT 120N.Furthermore, it may be possible that laser 130 outputs at a wavelengththat none of OLTs 120 are configured to receive, and therefore, wouldnot be able to determine that a wavelength rogue network interfacedevice exists in system 118 even if the wavelength rogue networkinterface device transmits optical signals at timeslots to which it isnot assigned.

In accordance with techniques described in this disclosure, one or moreof network interface devices 126 and 128 may be configured to implementthe self-quarantining technique, and as described in more detail, may beable to self-quarantine when transmitting at a wavelength that the OLTto which network interface devices 126 and 128 are assigned does notreceive. In this manner, even in instances where one of networkinterface devices 126 or 128 is a wavelength rogue network interfacedevice, it may be possible to quarantine such a wavelength rogue networkinterface device.

Again, a wavelength rogue network interface device may still receivedownstream optical signals, but may be transmitting upstream opticalsignals at an incorrect wavelength. The self-quarantine techniquesdescribed in this disclosure may allow a wavelength rogue networkinterface device to self-quarantine (e.g., disable upstreamtransmission) without necessarily affecting reception of downstreamoptical signals.

In accordance with some aspects of this disclosure, each one of OLTs 120may determine whether any optical signal was received during timeslotsassigned to respective ones of network interface devices 126 and 128.For example, assume that OLT 120A assigned a first timeslot to networkinterface device 126A, a second timeslot to network interface device126B, and so forth. OLT 120A may determine if OLT 120A received opticalsignal during the first timeslot, determine if OLT 120A received opticalsignal during the second timeslot, and so forth.

In this example, if OLT 120A does not receive optical signal from aparticular one of network interface devices 126 during its assignedtimeslot, OLT 120A may output information requesting that one of networkinterface device 126 to determine whether it is transmitting during itsassigned timeslot. For example, assume that network interface device126A did not transmit an optical signal during the first timeslot. Inthis case, OLT 120A may output a downstream signal requesting networkinterface device 126A to determine whether laser 130 transmitted anoptical signal during a timeslot assigned to network interface device126A.

In response, controller 136 may determine whether network interfacedevice 126A is transmitting optical signals during a timeslot assignedto network interface device 126A. For example, controller 136 may beconfigured with information indicating the timeslot when networkinterface device 126A should transmit upstream, and may also determinewhether network interface device 126A is to transmit upstream during aparticular timeslot. For example, if there is no information from thesubscriber devices coupled to network interface device 126A for upstreamtransmission, then controller 136 may determine that no upstreaminformation should be transmitted during a timeslot. Conversely, ifthere is information from the subscriber devices coupled to networkinterface device 126A for upstream transmission, then controller 136 maydetermine that upstream information should be transmitted during atimeslot.

Controller 136 may instruct monitor unit 134 to determine whether laser130 outputted an optical signal during a timeslot assigned to networkinterface device 126A. If controller 136 determines that laser 130transmitted an optical signal during a timeslot assigned to networkinterface device 126A, and controller 136 still received an instructionto determine whether network interface device 126A transmitted anoptical signal during its assigned timeslot, controller 136 maydetermine that laser 130 is not transmitting at the wavelength that OLT120A is configured to receive. Controller 136 may determine that networkinterface device 126A is a wavelength rogue network interface device andself-quarantine by disabling laser 130 from transmitting opticalsignals.

For instance, because controller 136 determined that laser 130transmitted an optical signal at an assigned timeslot, as indicated bythe optical power level value from monitor unit 134, but OLT 120Arequested controller 136 to determine whether network interface device126A transmitted an optical signal during an assigned timeslot,controller 136 may determine that OLT 120A did not receive an opticalsignal during the assigned timeslot because laser 130 is transmitting ata wavelength that OLT 120A does not receive. In this case, controller136 may quarantine network interface device 126A.

For a self-quarantined network interface device, such a quarantinednetwork interface device may be considered as a missing networkinterface device from the perspective of the OLT that is transmittingdownstream signals to the network interface device. For example, ifnetwork interface device 126A self-quarantines itself and OLT 120A doesnot receive information from network interface device 126A after OLT120A sends an instruction that OLT 120A did not receive upstreamcommunication from network interface device 126A, OLT 120A may considernetwork interface device 126A to be a missing network interface deviceand not transmit additional instructions indicating that OLT 120A didnot receive information from network interface device 126A.

In some examples, controller 136 may store information indicatingwhether laser 130 transmitted an optical signal during an assignedtimeslot. In these examples, if controller 136 receives a request fromOLT 120A to determine whether network interface device 126A transmittedan optical signal during the assigned timeslot, controller 136 maydetermine whether or not laser 130 transmitted an optical signal duringthe assigned timeslot based on the stored information. If controller 136determined that laser 130 did transmit an optical signal, thencontroller 136 may determine that OLT 120A did not receive the opticalsignal because network interface device 126A is a rogue networkinterface device. In some examples, for confirmation purposes,controller 136 may wait for multiple instances of OLT 120A requestingthat network interface device 126A determine whether it is transmittingduring its assigned timeslot before determining that network interfacedevice 126A is wavelength rogue.

Rather than or in addition to storing information indicating whetherlaser 130 transmitted an optical signal during a timeslot assigned tonetwork interface device 126A, controller 136 may wait until it receivesa request to determine whether network interface device 126A istransmitting an optical signal in its assigned timeslot. In this case,for the next timeslot, controller 136 may determine whether laser 130transmitted an optical signal based on the optical power level valueoutputted by monitor unit 134.

If laser 130 did transmit for the next timeslot, controller 136 maydetermine that laser 130 is transmitting at an incorrect wavelength(e.g., a wavelength that OLT 120A does not receive). However, this maylead to an incorrect diagnosis that laser 130 is transmitting at theincorrect wavelength. For instance, it may be possible that laser 130self-corrected by the time laser 130 needed to transmit the opticalsignal at the next timeslot. As another case, it may be possible thatthere was no upstream information to transmit in the previous timeslotthat led OLT 120A to indicate that no optical signal was received.Accordingly, in some examples, controller 136 may determine that networkinterface device 126A is a wavelength rogue network interface devicebased on multiple instances of OLT 120A indicating that no opticalsignal was received during timeslots assigned to network interfacedevice 126A.

In some examples, network interface device 126A may determine that it isa rogue network interface device without relying on monitor unit 134,and in these examples monitor unit 134 may not be needed. For instance,controller 136 may store information for all the times controller 136transmitted data to laser driver 132, or instructed laser driver 132 totransmit data. In these examples, if controller 136 receives informationthat OLT 120A did not receive data from network interface device 126Aduring its assigned timeslot, and controller 136 determined thatcontroller 136 instructed laser driver 132 to transmit, controller 136may determine that network interface device 126A is a rogue networkinterface device and self-quarantine network interface device 126A.

In some cases, monitor unit 134 may be able to determine the opticalpower level of the optical signal outputted by laser 130, but may not beable to determine the wavelength of the optical signal. Accordingly,monitor unit 134 may not be able to determine whether laser 130 istransmitting at the incorrect wavelength. However, in some examples, itmay be possible for monitor unit 134 to determine whether laser 130 istransmitting at the incorrect wavelength. For instance, monitor unit 134may be a tunable filter that receives optical signals reflected from theoutput of laser 130, and monitor unit 134 may be tuned to filter outoptical signals whose wavelength is not the wavelength at which OLT 120Areceives optical signals. In this case, if no optical signal passesthrough monitor unit 134, monitor unit 134 may output an optical outputpower level that is lower than a threshold, and controller 136 maydetermine that network interface device 126A is a wavelength roguenetwork interface device.

FIG. 12 is a flowchart illustrating an example method ofself-quarantining. For ease of description, FIG. 12 is described withrespect to network interface device 126A and OLT 120A. As illustrated inFIG. 12, controller 136 of network interface device 126A may receive oneor more requests from OLT 120A to determine whether network interfacedevice 126A, via laser 130, transmitted one or more optical signalsduring one or more timeslots assigned to network interface device 126Afor upstream transmission (138). Controller 136 of network interfacedevice 126A may determine that laser 130 of network interface device126A transmitted the one or more optical signals during one or moretimeslots assigned to the network interface device for upstreamtransmission (140).

For example, monitor unit 134 may monitor an optical output power levelof laser 130 during one or more of the timeslots assigned to networkinterface device 126A for upstream transmission. Controller 136 maydetermine that network interface device 126A transmitted the one or moreoptical signals during one or more timeslots assigned to networkinterface device 126A for upstream transmission based on the monitoring.

Furthermore, network interface device 126A may include a memoryconfigured to store information indicating when network interface device126A transmitted the one or more optical signals. In some examples,controller 136 may determine that network interface device 126Atransmitted the one or more optical signals during the one or moretimeslots assigned to network interface device 126A for upstreamtransmission based on the stored information. In some examples,controller 136 may determine that network interface device 126Atransmitted an optical signal for a timeslot of the timeslots followingthe reception of the request from OLT 120A.

Controller 136 may determine that network interface device 126A istransmitting the one or more optical signals at a wavelength that OLT120A does not receive based on the determination that network interfacedevice 126A transmitted the one or more optical signals during one ormore timeslots assigned to network interface device 126A for upstreamtransmission, and the reception of the one or more requests from OLT120A (142). Controller 136 may disable network interface device 126Afrom transmitting upstream optical signals based on the determinationthat network interface device 126A is transmitting the one or moreoptical signals at the wavelength that OLT 120A does not receive (144).

In some examples, to confirm that network interface device 126A is awavelength rogue network interface device, controller 136 may determinemultiple instances of cases where network interface device 126Atransmitted optical signals, but OLT 120A did not receive. For instance,controller 136 may receive a plurality of requests from OLT 120A.Controller 136 may also determine that network interface device 126Atransmitted the one or more optical signals during a plurality oftimeslots assigned to the network interface device for upstreamtransmission, and determine that network interface device 126A istransmitting the one or more optical signals at a wavelength that OLT120A does not receive based on the determination that network interfacedevice 126A transmitted the plurality of optical signals during one ormore timeslots assigned to network interface device 126A for upstreamtransmission, and the reception of the plurality of requests from OLT120A.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over, as oneor more instructions or code, a computer-readable medium and executed bya hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media. In this manner, computer-readable mediagenerally may correspond to tangible computer-readable storage mediawhich is non-transitory. Data storage media may be any available mediathat can be accessed by one or more computers or one or more processorsto retrieve instructions, code and/or data structures for implementationof the techniques described in this disclosure. A computer programproduct may include a computer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. It should be understood that computer-readablestorage media and data storage media do not include carrier waves,signals, or other transient media, but are instead directed tonon-transient, tangible storage media. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc, where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

Instructions may be executed by one or more processors (e.g., processor44 or controller 32), such as one or more digital signal processors(DSPs), general purpose microprocessors, application specific integratedcircuits (ASICs), field programmable logic arrays (FPGAs), or otherequivalent integrated or discrete logic circuitry. Accordingly, the term“processor” or “controller” as used herein may refer to any of theforegoing structure or any other structure suitable for implementationof the techniques described herein. Also, the techniques could be fullyimplemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including an integrated circuit (IC) or a setof ICs (e.g., a chip set). Various components, modules, or units aredescribed in this disclosure to emphasize functional aspects of devicesconfigured to perform the disclosed techniques, but do not necessarilyrequire realization by different hardware units. Rather, as describedabove, various units may be combined in a hardware unit or provided by acollection of interoperative hardware units, including one or moreprocessors as described above, in conjunction with suitable softwareand/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method comprising: receiving, with a networkinterface device, one or more requests from an optical line terminal(OLT) to determine whether the network interface device transmitted oneor more optical signals during one or more timeslots assigned to thenetwork interface device for upstream transmission; determining, withthe network interface device, that the network interface devicetransmitted the one or more optical signals during one or more timeslotsassigned to the network interface device for upstream transmission;determining that the network interface device is transmitting the one ormore optical signals at a wavelength that the OLT does not receive basedon the determination that the network interface device transmitted theone or more optical signals during one or more timeslots assigned to thenetwork interface device for upstream transmission, and the reception ofthe one or more requests from the OLT; and disabling the networkinterface device from transmitting upstream optical signals based on thedetermination that the network interface device is transmitting the oneor more optical signals at the wavelength that the OLT does not receive.2. The method of claim 1, further comprising: monitoring an opticaloutput power level of a laser coupled to the network interface deviceduring one or more of the timeslots assigned to the network interfacedevice for upstream transmission, wherein determining that the networkinterface device transmitted the one or more optical signals during oneor more timeslots assigned to the network interface device for upstreamtransmission comprises determining that the network interface devicetransmitted the one or more optical signals during one or more timeslotsassigned to the network interface device for upstream transmission basedon the monitoring of the optical output power level.
 3. The method ofclaim 1, further comprising: storing information indicating when thenetwork interface device transmitted the one or more optical signals,wherein determining that the network interface device transmitted theone or more optical signals during the one or more timeslots assigned tothe network interface device for upstream transmission comprisesdetermining that the network interface device transmitted the one ormore optical signals during the one or more timeslots assigned to thenetwork interface device for upstream transmission based on the storedinformation.
 4. The method of claim 1, wherein determining that thenetwork interface device transmitted the one or more optical signalsduring one or more timeslots assigned to the network interface devicefor upstream transmission comprises determining that the networkinterface device transmitted an optical signal for a timeslot of thetimeslots following the reception of the request from the OLT.
 5. Themethod of claim 1, wherein receiving the one or more requests comprisesreceiving a plurality of requests from the OLT, wherein determining thatthe network interface device transmitted the one or more optical signalsduring one or more timeslots assigned to the network interface devicefor upstream transmission comprises determining that the networkinterface device transmitted the one or more optical signals during aplurality of timeslots assigned to the network interface device forupstream transmission, and wherein determining that the networkinterface device is transmitting the one or more optical signals at awavelength that the OLT does not receive comprises determining that thenetwork interface device is transmitting the one or more optical signalsat a wavelength that the OLT does not receive based on the determinationthat the network interface device transmitted the plurality of opticalsignals during one or more timeslots assigned to the network interfacedevice for upstream transmission, and the reception of the plurality ofrequests from the OLT.
 6. A network interface device comprising: alaser; and a controller configured to: receive one or more requests froman optical line terminal (OLT) to determine whether the lasertransmitted one or more optical signals during one or more timeslotsassigned to the network interface device for upstream transmission;determine that the laser transmitted the one or more optical signalsduring one or more timeslots assigned to the network interface devicefor upstream transmission; determine that the laser is transmitting theone or more optical signals at a wavelength that the OLT does notreceive based on the determination that the laser transmitted the one ormore optical signals during one or more timeslots assigned to thenetwork interface device for upstream transmission, and the reception ofthe one or more requests from the OLT; and disable the network interfacedevice from transmitting upstream optical signals based on thedetermination that the laser is transmitting the one or more opticalsignals at the wavelength that the OLT does not receive.
 7. The networkinterface device of claim 6, further comprising: a monitor unitconfigured to monitor an optical output power level of the laser duringone or more of the timeslots assigned to the network interface devicefor upstream transmission, and transmit information indicating theoptical output power level to the controller, wherein to determine thatthe laser transmitted the one or more optical signals during one or moretimeslots assigned to the network interface device for upstreamtransmission, the controller is configured to determine that the lasertransmitted the one or more optical signals during one or more timeslotsassigned to the network interface device for upstream transmission basedon the optical power level transmitted by the monitor unit.
 8. Thenetwork interface device of claim 6, further comprising: a memoryconfigured to store information indicating when the laser transmittedthe one or more optical signals, wherein to determine that the lasertransmitted the one or more optical signals during the one or moretimeslots assigned to the network interface device for upstreamtransmission, the controller is configured to determine that the lasertransmitted the one or more optical signals during the one or moretimeslots assigned to the network interface device for upstreamtransmission based on the stored information.
 9. The network interfacedevice of claim 6, wherein to determine that the laser transmitted theone or more optical signals during one or more timeslots assigned to thenetwork interface device for upstream transmission, the controller isconfigured to determine that the laser transmitted an optical signal fora timeslot of the timeslots following the reception of the request fromthe OLT.
 10. The network interface device of claim 6, wherein to receivethe one or more requests, the controller is configured to receive aplurality of requests from the OLT, wherein to determine that the lasertransmitted the one or more optical signals during one or more timeslotsassigned to the network interface device for upstream transmission, thecontroller is configured to determine that the laser transmitted the oneor more optical signals during a plurality of timeslots assigned to thenetwork interface device for upstream transmission, and wherein todetermine that the laser is transmitting the one or more optical signalsat a wavelength that the OLT does not receive, the controller isconfigured to determine that the laser is transmitting the one or moreoptical signals at a wavelength that the OLT does not receive based onthe determination that the laser transmitted the plurality of opticalsignals during one or more timeslots assigned to the network interfacedevice for upstream transmission, and the reception of the plurality ofrequests from the OLT.
 11. A network interface device comprising: meansfor receiving one or more requests from an optical line terminal (OLT)to determine whether the network interface device transmitted one ormore optical signals during one or more timeslots assigned to thenetwork interface device for upstream transmission; means fordetermining that the network interface device transmitted the one ormore optical signals during one or more timeslots assigned to thenetwork interface device for upstream transmission; means fordetermining that the network interface device is transmitting the one ormore optical signals at a wavelength that the OLT does not receive basedon the determination that the network interface device transmitted theone or more optical signals during one or more timeslots assigned to thenetwork interface device for upstream transmission, and the reception ofthe one or more requests from the OLT; and means for disabling thenetwork interface device from transmitting upstream optical signalsbased on the determination that the network interface device istransmitting the one or more optical signals at the wavelength that theOLT does not receive.
 12. The network interface device of claim 11,further comprising: means for monitoring an optical output power levelof a laser coupled to the network interface device during one or more ofthe timeslots assigned to the network interface device for upstreamtransmission, wherein the means for determining that the networkinterface device transmitted the one or more optical signals during oneor more timeslots assigned to the network interface device for upstreamtransmission comprises means for determining that the network interfacedevice transmitted the one or more optical signals during one or moretimeslots assigned to the network interface device for upstreamtransmission based on the monitoring of the optical output power level.13. The network interface device of claim 11, further comprising: meansfor storing information indicating when the network interface devicetransmitted the one or more optical signals, wherein the means fordetermining that the network interface device transmitted the one ormore optical signals during the one or more timeslots assigned to thenetwork interface device for upstream transmission comprises means fordetermining that the network interface device transmitted the one ormore optical signals during the one or more timeslots assigned to thenetwork interface device for upstream transmission based on the storedinformation.
 14. The network interface device of claim 11, wherein themeans for determining that the network interface device transmitted theone or more optical signals during one or more timeslots assigned to thenetwork interface device for upstream transmission comprises means fordetermining that the network interface device transmitted an opticalsignal for a timeslot of the timeslots following the reception of therequest from the OLT.
 15. The network interface device of claim 11,wherein the means for receiving the one or more requests comprises meansfor receiving a plurality of requests from the OLT, wherein the meansfor determining that the network interface device transmitted the one ormore optical signals during one or more timeslots assigned to thenetwork interface device for upstream transmission comprises means fordetermining that the network interface device transmitted the one ormore optical signals during a plurality of timeslots assigned to thenetwork interface device for upstream transmission, and wherein themeans for determining that the network interface device is transmittingthe one or more optical signals at a wavelength that the OLT does notreceive comprises means for determining that the network interfacedevice is transmitting the one or more optical signals at a wavelengththat the OLT does not receive based on the determination that thenetwork interface device transmitted the plurality of optical signalsduring one or more timeslots assigned to the network interface devicefor upstream transmission, and the reception of the plurality ofrequests from the OLT.
 16. A computer-readable storage medium havinginstructions stored thereon that when executed cause a controller of anetwork interface device to: receive one or more requests from anoptical line terminal (OLT) to determine whether the network interfacedevice transmitted one or more optical signals during one or moretimeslots assigned to the network interface device for upstreamtransmission; determine that the network interface device transmittedthe one or more optical signals during one or more timeslots assigned tothe network interface device for upstream transmission; determine thatthe network interface device is transmitting the one or more opticalsignals at a wavelength that the OLT does not receive based on thedetermination that the network interface device transmitted the one ormore optical signals during one or more timeslots assigned to thenetwork interface device for upstream transmission, and the reception ofthe one or more requests from the OLT; and disable the network interfacedevice from transmitting upstream optical signals based on thedetermination that the network interface device is transmitting the oneor more optical signals at the wavelength that the OLT does not receive.